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What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

• What is the purpose of literature review? 
• a. Habitat Loss and Species Extinction: 
• b. Range Shifts and Phenological Changes: 
• c. Ocean Acidification and Coral Reefs: 
• d. Adaptive Strategies and Conservation Efforts: 
• How to write a good literature review 
• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• Frequently asked questions 

What is a literature review?

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

What is the purpose of literature review?

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

• Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 
• Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field. 
• Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 
• Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 
• Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 
• Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

a. Habitat Loss and Species Extinction:

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

b. Range Shifts and Phenological Changes:

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

c. Ocean Acidification and Coral Reefs:

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

d. Adaptive Strategies and Conservation Efforts:

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

How to write a good literature review

Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. 

Frequently asked questions

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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How To Write A Literature Review - A Complete Guide

Table of Contents

A literature review is much more than just another section in your research paper. It forms the very foundation of your research. It is a formal piece of writing where you analyze the existing theoretical framework, principles, and assumptions and use that as a base to shape your approach to the research question.

Curating and drafting a solid literature review section not only lends more credibility to your research paper but also makes your research tighter and better focused. But, writing literature reviews is a difficult task. It requires extensive reading, plus you have to consider market trends and technological and political changes, which tend to change in the blink of an eye.

Now streamline your literature review process with the help of SciSpace Copilot. With this AI research assistant, you can efficiently synthesize and analyze a vast amount of information, identify key themes and trends, and uncover gaps in the existing research. Get real-time explanations, summaries, and answers to your questions for the paper you're reviewing, making navigating and understanding the complex literature landscape easier.

In this comprehensive guide, we will explore everything from the definition of a literature review, its appropriate length, various types of literature reviews, and how to write one.

What is a literature review?

A literature review is a collation of survey, research, critical evaluation, and assessment of the existing literature in a preferred domain.

Eminent researcher and academic Arlene Fink, in her book Conducting Research Literature Reviews , defines it as the following:

“A literature review surveys books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated.

Literature reviews are designed to provide an overview of sources you have explored while researching a particular topic, and to demonstrate to your readers how your research fits within a larger field of study.”

Simply put, a literature review can be defined as a critical discussion of relevant pre-existing research around your research question and carving out a definitive place for your study in the existing body of knowledge. Literature reviews can be presented in multiple ways: a section of an article, the whole research paper itself, or a chapter of your thesis.

A literature review does function as a summary of sources, but it also allows you to analyze further, interpret, and examine the stated theories, methods, viewpoints, and, of course, the gaps in the existing content.

As an author, you can discuss and interpret the research question and its various aspects and debate your adopted methods to support the claim.

What is the purpose of a literature review?

A literature review is meant to help your readers understand the relevance of your research question and where it fits within the existing body of knowledge. As a researcher, you should use it to set the context, build your argument, and establish the need for your study.

What is the importance of a literature review?

The literature review is a critical part of research papers because it helps you:

• Gain an in-depth understanding of your research question and the surrounding area
• Convey that you have a thorough understanding of your research area and are up-to-date with the latest changes and advancements
• Establish how your research is connected or builds on the existing body of knowledge and how it could contribute to further research
• Elaborate on the validity and suitability of your theoretical framework and research methodology
• Identify and highlight gaps and shortcomings in the existing body of knowledge and how things need to change
• Convey to readers how your study is different or how it contributes to the research area

How long should a literature review be?

Ideally, the literature review should take up 15%-40% of the total length of your manuscript. So, if you have a 10,000-word research paper, the minimum word count could be 1500.

Your literature review format depends heavily on the kind of manuscript you are writing — an entire chapter in case of doctoral theses, a part of the introductory section in a research article, to a full-fledged review article that examines the previously published research on a topic.

Another determining factor is the type of research you are doing. The literature review section tends to be longer for secondary research projects than primary research projects.

What are the different types of literature reviews?

All literature reviews are not the same. There are a variety of possible approaches that you can take. It all depends on the type of research you are pursuing.

Here are the different types of literature reviews:

Argumentative review

It is called an argumentative review when you carefully present literature that only supports or counters a specific argument or premise to establish a viewpoint.

Integrative review

It is a type of literature review focused on building a comprehensive understanding of a topic by combining available theoretical frameworks and empirical evidence.

Methodological review

This approach delves into the ''how'' and the ''what" of the research question —  you cannot look at the outcome in isolation; you should also review the methodology used.

Systematic review

This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research and collect, report, and analyze data from the studies included in the review.

Meta-analysis review

Meta-analysis uses statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analysis can provide more precise estimates of the effects than those derived from the individual studies included within a review.

Historical review

Historical literature reviews focus on examining research throughout a period, often starting with the first time an issue, concept, theory, or phenomenon emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and identify future research's likely directions.

Theoretical Review

This form aims to examine the corpus of theory accumulated regarding an issue, concept, theory, and phenomenon. The theoretical literature review helps to establish what theories exist, the relationships between them, the degree the existing approaches have been investigated, and to develop new hypotheses to be tested.

Scoping Review

The Scoping Review is often used at the beginning of an article, dissertation, or research proposal. It is conducted before the research to highlight gaps in the existing body of knowledge and explains why the project should be greenlit.

State-of-the-Art Review

The State-of-the-Art review is conducted periodically, focusing on the most recent research. It describes what is currently known, understood, or agreed upon regarding the research topic and highlights where there are still disagreements.

Can you use the first person in a literature review?

When writing literature reviews, you should avoid the usage of first-person pronouns. It means that instead of "I argue that" or "we argue that," the appropriate expression would be "this research paper argues that."

Do you need an abstract for a literature review?

Ideally, yes. It is always good to have a condensed summary that is self-contained and independent of the rest of your review. As for how to draft one, you can follow the same fundamental idea when preparing an abstract for a literature review. It should also include:

• The research topic and your motivation behind selecting it
• A one-sentence thesis statement
• An explanation of the kinds of literature featured in the review
• Summary of what you've learned
• Conclusions you drew from the literature you reviewed
• Potential implications and future scope for research

Here's an example of the abstract of a literature review

Is a literature review written in the past tense?

Yes, the literature review should ideally be written in the past tense. You should not use the present or future tense when writing one. The exceptions are when you have statements describing events that happened earlier than the literature you are reviewing or events that are currently occurring; then, you can use the past perfect or present perfect tenses.

How many sources for a literature review?

There are multiple approaches to deciding how many sources to include in a literature review section. The first approach would be to look level you are at as a researcher. For instance, a doctoral thesis might need 60+ sources. In contrast, you might only need to refer to 5-15 sources at the undergraduate level.

The second approach is based on the kind of literature review you are doing — whether it is merely a chapter of your paper or if it is a self-contained paper in itself. When it is just a chapter, sources should equal the total number of pages in your article's body. In the second scenario, you need at least three times as many sources as there are pages in your work.

Quick tips on how to write a literature review

To know how to write a literature review, you must clearly understand its impact and role in establishing your work as substantive research material.

You need to follow the below-mentioned steps, to write a literature review:

• Outline the purpose behind the literature review
• Search relevant literature
• Examine and assess the relevant resources
• Discover connections by drawing deep insights from the resources
• Structure planning to write a good literature review

1. Outline and identify the purpose of  a literature review

As a first step on how to write a literature review, you must know what the research question or topic is and what shape you want your literature review to take. Ensure you understand the research topic inside out, or else seek clarifications. You must be able to the answer below questions before you start:

• How many sources do I need to include?
• What kind of sources should I analyze?
• How much should I critically evaluate each source?
• Should I summarize, synthesize or offer a critique of the sources?
• Do I need to include any background information or definitions?

Additionally, you should know that the narrower your research topic is, the swifter it will be for you to restrict the number of sources to be analyzed.

2. Search relevant literature

Dig deeper into search engines to discover what has already been published around your chosen topic. Make sure you thoroughly go through appropriate reference sources like books, reports, journal articles, government docs, and web-based resources.

You must prepare a list of keywords and their different variations. You can start your search from any library’s catalog, provided you are an active member of that institution. The exact keywords can be extended to widen your research over other databases and academic search engines like:

• Google Scholar
• Microsoft Academic
• Science.gov

Besides, it is not advisable to go through every resource word by word. Alternatively, what you can do is you can start by reading the abstract and then decide whether that source is relevant to your research or not.

Additionally, you must spend surplus time assessing the quality and relevance of resources. It would help if you tried preparing a list of citations to ensure that there lies no repetition of authors, publications, or articles in the literature review.

3. Examine and assess the sources

It is nearly impossible for you to go through every detail in the research article. So rather than trying to fetch every detail, you have to analyze and decide which research sources resemble closest and appear relevant to your chosen domain.

While analyzing the sources, you should look to find out answers to questions like:

• What question or problem has the author been describing and debating?
• What is the definition of critical aspects?
• How well the theories, approach, and methodology have been explained?
• Whether the research theory used some conventional or new innovative approach?
• How relevant are the key findings of the work?
• In what ways does it relate to other sources on the same topic?
• What challenges does this research paper pose to the existing theory
• What are the possible contributions or benefits it adds to the subject domain?

Be always mindful that you refer only to credible and authentic resources. It would be best if you always take references from different publications to validate your theory.

Always keep track of important information or data you can present in your literature review right from the beginning. It will help steer your path from any threats of plagiarism and also make it easier to curate an annotated bibliography or reference section.

4. Discover connections

At this stage, you must start deciding on the argument and structure of your literature review. To accomplish this, you must discover and identify the relations and connections between various resources while drafting your abstract.

A few aspects that you should be aware of while writing a literature review include:

• Rise to prominence: Theories and methods that have gained reputation and supporters over time.
• Constant scrutiny: Concepts or theories that repeatedly went under examination.
• Contradictions and conflicts: Theories, both the supporting and the contradictory ones, for the research topic.
• Knowledge gaps: What exactly does it fail to address, and how to bridge them with further research?
• Influential resources: Significant research projects available that have been upheld as milestones or perhaps, something that can modify the current trends

Once you join the dots between various past research works, it will be easier for you to draw a conclusion and identify your contribution to the existing knowledge base.

5. Structure planning to write a good literature review

There exist different ways towards planning and executing the structure of a literature review. The format of a literature review varies and depends upon the length of the research.

Like any other research paper, the literature review format must contain three sections: introduction, body, and conclusion. The goals and objectives of the research question determine what goes inside these three sections.

Nevertheless, a good literature review can be structured according to the chronological, thematic, methodological, or theoretical framework approach.

Literature review samples

1. Standalone

2. As a section of a research paper

How SciSpace Discover makes literature review a breeze?

SciSpace Discover is a one-stop solution to do an effective literature search and get barrier-free access to scientific knowledge. It is an excellent repository where you can find millions of only peer-reviewed articles and full-text PDF files. Here’s more on how you can use it:

Find the right information

Find what you want quickly and easily with comprehensive search filters that let you narrow down papers according to PDF availability, year of publishing, document type, and affiliated institution. Moreover, you can sort the results based on the publishing date, citation count, and relevance.

Assess credibility of papers quickly

When doing the literature review, it is critical to establish the quality of your sources. They form the foundation of your research. SciSpace Discover helps you assess the quality of a source by providing an overview of its references, citations, and performance metrics.

Get the complete picture in no time

SciSpace Discover’s personalized suggestion engine helps you stay on course and get the complete picture of the topic from one place. Every time you visit an article page, it provides you links to related papers. Besides that, it helps you understand what’s trending, who are the top authors, and who are the leading publishers on a topic.

Make referring sources super easy

To ensure you don't lose track of your sources, you must start noting down your references when doing the literature review. SciSpace Discover makes this step effortless. Click the 'cite' button on an article page, and you will receive preloaded citation text in multiple styles — all you've to do is copy-paste it into your manuscript.

Final tips on how to write a literature review

A massive chunk of time and effort is required to write a good literature review. But, if you go about it systematically, you'll be able to save a ton of time and build a solid foundation for your research.

We hope this guide has helped you answer several key questions you have about writing literature reviews.

Would you like to explore SciSpace Discover and kick off your literature search right away? You can get started here .

Frequently Asked Questions (FAQs)

1. how to start a literature review.

• What questions do you want to answer?

• What sources do you need to answer these questions?

• What information do these sources contain?

• How can you use this information to answer your questions?

2. What to include in a literature review?

• A brief background of the problem or issue

• What has previously been done to address the problem or issue

• A description of what you will do in your project

• How this study will contribute to research on the subject

3. Why literature review is important?

The literature review is an important part of any research project because it allows the writer to look at previous studies on a topic and determine existing gaps in the literature, as well as what has already been done. It will also help them to choose the most appropriate method for their own study.

4. How to cite a literature review in APA format?

To cite a literature review in APA style, you need to provide the author's name, the title of the article, and the year of publication. For example: Patel, A. B., & Stokes, G. S. (2012). The relationship between personality and intelligence: A meta-analysis of longitudinal research. Personality and Individual Differences, 53(1), 16-21

5. What are the components of a literature review?

• A brief introduction to the topic, including its background and context. The introduction should also include a rationale for why the study is being conducted and what it will accomplish.

• A description of the methodologies used in the study. This can include information about data collection methods, sample size, and statistical analyses.

• A presentation of the findings in an organized format that helps readers follow along with the author's conclusions.

6. What are common errors in writing literature review?

• Not spending enough time to critically evaluate the relevance of resources, observations and conclusions.

• Totally relying on secondary data while ignoring primary data.

• Letting your personal bias seep into your interpretation of existing literature.

• No detailed explanation of the procedure to discover and identify an appropriate literature review.

7. What are the 5 C's of writing literature review?

• Cite - the sources you utilized and referenced in your research.

• Compare - existing arguments, hypotheses, methodologies, and conclusions found in the knowledge base.

• Contrast - the arguments, topics, methodologies, approaches, and disputes that may be found in the literature.

• Critique - the literature and describe the ideas and opinions you find more convincing and why.

• Connect - the various studies you reviewed in your research.

8. How many sources should a literature review have?

When it is just a chapter, sources should equal the total number of pages in your article's body. if it is a self-contained paper in itself, you need at least three times as many sources as there are pages in your work.

9. Can literature review have diagrams?

• To represent an abstract idea or concept

• To explain the steps of a process or procedure

• To help readers understand the relationships between different concepts

10. How old should sources be in a literature review?

Sources for a literature review should be as current as possible or not older than ten years. The only exception to this rule is if you are reviewing a historical topic and need to use older sources.

11. What are the types of literature review?

• Argumentative review

• Integrative review

• Methodological review

• Systematic review

• Meta-analysis review

• Historical review

• Theoretical review

• Scoping review

• State-of-the-Art review

12. Is a literature review mandatory?

Yes. Literature review is a mandatory part of any research project. It is a critical step in the process that allows you to establish the scope of your research, and provide a background for the rest of your work.

But before you go,

• Six Online Tools for Easy Literature Review
• Evaluating literature review: systematic vs. scoping reviews
• Systematic Approaches to a Successful Literature Review
• Writing Integrative Literature Reviews: Guidelines and Examples

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• What is a Literature Review? | Guide, Template, & Examples

What is a Literature Review? | Guide, Template, & Examples

Published on 22 February 2022 by Shona McCombes . Revised on 7 June 2022.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research.

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarise sources – it analyses, synthesises, and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

Why write a literature review, examples of literature reviews, step 1: search for relevant literature, step 2: evaluate and select sources, step 3: identify themes, debates and gaps, step 4: outline your literature review’s structure, step 5: write your literature review, frequently asked questions about literature reviews, introduction.

• Quick Run-through
• Step 1 & 2

When you write a dissertation or thesis, you will have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and scholarly context
• Develop a theoretical framework and methodology for your research
• Position yourself in relation to other researchers and theorists
• Show how your dissertation addresses a gap or contributes to a debate

You might also have to write a literature review as a stand-alone assignment. In this case, the purpose is to evaluate the current state of research and demonstrate your knowledge of scholarly debates around a topic.

The content will look slightly different in each case, but the process of conducting a literature review follows the same steps. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research objectives and questions .

If you are writing a literature review as a stand-alone assignment, you will have to choose a focus and develop a central question to direct your search. Unlike a dissertation research question, this question has to be answerable without collecting original data. You should be able to answer it based only on a review of existing publications.

Make a list of keywords

Start by creating a list of keywords related to your research topic. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list if you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can use boolean operators to help narrow down your search:

Read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

To identify the most important publications on your topic, take note of recurring citations. If the same authors, books or articles keep appearing in your reading, make sure to seek them out.

You probably won’t be able to read absolutely everything that has been written on the topic – you’ll have to evaluate which sources are most relevant to your questions.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models and methods? Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• How does the publication contribute to your understanding of the topic? What are its key insights and arguments?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible, and make sure you read any landmark studies and major theories in your field of research.

You can find out how many times an article has been cited on Google Scholar – a high citation count means the article has been influential in the field, and should certainly be included in your literature review.

The scope of your review will depend on your topic and discipline: in the sciences you usually only review recent literature, but in the humanities you might take a long historical perspective (for example, to trace how a concept has changed in meaning over time).

Remember that you can use our template to summarise and evaluate sources you’re thinking about using!

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It’s important to keep track of your sources with references to avoid plagiarism . It can be helpful to make an annotated bibliography, where you compile full reference information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

You can use our free APA Reference Generator for quick, correct, consistent citations.

Prevent plagiarism, run a free check.

To begin organising your literature review’s argument and structure, you need to understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly-visual platforms like Instagram and Snapchat – this is a gap that you could address in your own research.

There are various approaches to organising the body of a literature review. You should have a rough idea of your strategy before you start writing.

Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarising sources in order.

Try to analyse patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organise your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text, your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

If you are writing the literature review as part of your dissertation or thesis, reiterate your central problem or research question and give a brief summary of the scholarly context. You can emphasise the timeliness of the topic (“many recent studies have focused on the problem of x”) or highlight a gap in the literature (“while there has been much research on x, few researchers have taken y into consideration”).

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, make sure to follow these tips:

• Summarise and synthesise: give an overview of the main points of each source and combine them into a coherent whole.
• Analyse and interpret: don’t just paraphrase other researchers – add your own interpretations, discussing the significance of findings in relation to the literature as a whole.
• Critically evaluate: mention the strengths and weaknesses of your sources.
• Write in well-structured paragraphs: use transitions and topic sentences to draw connections, comparisons and contrasts.

In the conclusion, you should summarise the key findings you have taken from the literature and emphasise their significance.

If the literature review is part of your dissertation or thesis, reiterate how your research addresses gaps and contributes new knowledge, or discuss how you have drawn on existing theories and methods to build a framework for your research. This can lead directly into your methodology section.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a dissertation , thesis, research paper , or proposal .

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarise yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your  dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

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Database search tip : Add the phrase "literature review" to your search to find published literature reviews.

While at the GSD, you may be asked to conduct a literature review for research courses or if you are writing a thesis or dissertation.

What is a literature review? 

It is a survey of relevant or foundational texts about a particular topic, theory, or research question.  A literature review

May provide the background for larger work, or it may stand on its own.  

Is more than a simple list of sources; an effective literature review analyzes and synthesizes information about key themes or issues. 

Contains a set of themes fundamental enough to be considered a reasonable mode of entry into the field along with the relevant, foundational texts of that field or sub-field.

 Coheres around a chronological, geographic, technical, and/or cultural structure.

Is thorough but not comprehensive; it is impossible to reach an exhaustive knowledge of a field, especially as a graduate student.

How do you conduct a literature review?  

 Gather Sources through preliminary research 

• This step allows you to discover what has been written about in the field 
• Focus your topic:  A literature review aims to cover all of the research on a given topic. If the topic is too large, there will be too much material to cover it adequately.   

The GSD’s guidelines for doctoral literature reviews offers helpful examples of feasible topics:

A research area usually covers a relatively broad field like the ‘history of architecture from 1800 to the present,’ the ‘theories of urbanization in the nineteenth and twentieth centuries,’ or ‘digital fabrication.’ More focused major fields are of course possible and could include studies of ‘Decorative Art, Design and the Object: History, Theory, and Debate: 1850-1930,’ ‘Modernity and Modernism in Latin America,’ or ‘Life Cycle Design.’ 

• Read with a purpose:  Although you will need to briefly summarize sources, a good literature review requires that you isolate key themes or issues related to your own research interests.  

 Evaluate Sources 

Conduct a critical appraisal to evaluate the literature and what has been done already to see the gaps in the field, thus what still needs to be done in one’s own research 

For each book or article consider: Is the author an expert? Does the evidence support the conclusion? Is the argument or evidence complete?  

Does all research arrive at the same conclusion or are there differing opinions?  What evidence or reasoning are the differences based on? What questions are raised by the literature? Are there any gaps or omissions? 

 Write an Introduction 

• The introduction should identify your topic, some discussion of the significance of that topic and a thesis statement that outlines what conclusion you will draw from your analysis and synthesis of the literature. If your literature review is part of a larger work, explain the importance of the review to your research question. 
• Focus on the organizing principles of your literature review. How have you organized your sources?  

Have you organized it by theme? This is the most common way to organize literature reviews as it relates each source back to the field.  

Have you organized it by methodology? This is often used when discussing interdisciplinary approaches to a topic or when discussing a number of studies with a different approach. 

Have you organized it by chronology? This method is helpful when historical changes are central to explaining the topic. 

Write the body  

• The body will be comprised of your findings from evaluating the sources. In the body, discuss and assess the research according to the specific organizational principles above.  
• Focus on the relationship of sources to each other: how do these sources constitute a field?  
• Return to your evaluations and critical appraisals of the texts. Include these appraisals in the body of your literature review.  
• Articulate the relevance of these sources to your research question.  
• Demonstrate that your research and source selection is sufficient to constitute a reasonable mode of entry into the particular field where you what to conduct subsequent research.  

Write the conclusion 

• This section is perhaps the most important: you should briefly outline all gaps in the field and assess what is lacking in the current field of literature. Thus, you establish the value of your research and where you will situate your research within the context that you have explored in the body. 
• Literature Review Concise information from the Writing Centre, University of Toronto at Scarborough.
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• Literature Review: The What, Why and How-to Guide
• Introduction

Literature Review: The What, Why and How-to Guide — Introduction

• Getting Started
• How to Pick a Topic
• Strategies to Find Sources
• Evaluating Sources & Lit. Reviews
• Tips for Writing Literature Reviews
• Writing Literature Review: Useful Sites
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• Other Academic Writings

What are Literature Reviews?

So, what is a literature review? "A literature review is an account of what has been published on a topic by accredited scholars and researchers. In writing the literature review, your purpose is to convey to your reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. As a piece of writing, the literature review must be defined by a guiding concept (e.g., your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries." Taylor, D.  The literature review: A few tips on conducting it . University of Toronto Health Sciences Writing Centre.

Goals of Literature Reviews

What are the goals of creating a Literature Review?  A literature could be written to accomplish different aims:

• To develop a theory or evaluate an existing theory
• To summarize the historical or existing state of a research topic
• Identify a problem in a field of research 

Baumeister, R. F., & Leary, M. R. (1997). Writing narrative literature reviews .  Review of General Psychology , 1 (3), 311-320.

What kinds of sources require a Literature Review?

• A research paper assigned in a course
• A thesis or dissertation
• A grant proposal
• An article intended for publication in a journal

All these instances require you to collect what has been written about your research topic so that you can demonstrate how your own research sheds new light on the topic.

Types of Literature Reviews

What kinds of literature reviews are written?

Narrative review: The purpose of this type of review is to describe the current state of the research on a specific topic/research and to offer a critical analysis of the literature reviewed. Studies are grouped by research/theoretical categories, and themes and trends, strengths and weakness, and gaps are identified. The review ends with a conclusion section which summarizes the findings regarding the state of the research of the specific study, the gaps identify and if applicable, explains how the author's research will address gaps identify in the review and expand the knowledge on the topic reviewed.

• Example : Predictors and Outcomes of U.S. Quality Maternity Leave: A Review and Conceptual Framework:  10.1177/08948453211037398  

Systematic review : "The authors of a systematic review use a specific procedure to search the research literature, select the studies to include in their review, and critically evaluate the studies they find." (p. 139). Nelson, L. K. (2013). Research in Communication Sciences and Disorders . Plural Publishing.

• Example : The effect of leave policies on increasing fertility: a systematic review:  10.1057/s41599-022-01270-w

Meta-analysis : "Meta-analysis is a method of reviewing research findings in a quantitative fashion by transforming the data from individual studies into what is called an effect size and then pooling and analyzing this information. The basic goal in meta-analysis is to explain why different outcomes have occurred in different studies." (p. 197). Roberts, M. C., & Ilardi, S. S. (2003). Handbook of Research Methods in Clinical Psychology . Blackwell Publishing.

• Example : Employment Instability and Fertility in Europe: A Meta-Analysis:  10.1215/00703370-9164737

Meta-synthesis : "Qualitative meta-synthesis is a type of qualitative study that uses as data the findings from other qualitative studies linked by the same or related topic." (p.312). Zimmer, L. (2006). Qualitative meta-synthesis: A question of dialoguing with texts .  Journal of Advanced Nursing , 53 (3), 311-318.

• Example : Women’s perspectives on career successes and barriers: A qualitative meta-synthesis:  10.1177/05390184221113735

Literature Reviews in the Health Sciences

• UConn Health subject guide on systematic reviews Explanation of the different review types used in health sciences literature as well as tools to help you find the right review type
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• Last Updated: Sep 21, 2022 2:16 PM
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• 04 December 2020
• Correction 09 December 2020

How to write a superb literature review

Andy Tay is a freelance writer based in Singapore.

You can also search for this author in PubMed   Google Scholar

Literature reviews are important resources for scientists. They provide historical context for a field while offering opinions on its future trajectory. Creating them can provide inspiration for one’s own research, as well as some practice in writing. But few scientists are trained in how to write a review — or in what constitutes an excellent one. Even picking the appropriate software to use can be an involved decision (see ‘Tools and techniques’). So Nature asked editors and working scientists with well-cited reviews for their tips.

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doi: https://doi.org/10.1038/d41586-020-03422-x

Interviews have been edited for length and clarity.

Updates & Corrections

Correction 09 December 2020 : An earlier version of the tables in this article included some incorrect details about the programs Zotero, Endnote and Manubot. These have now been corrected.

Hsing, I.-M., Xu, Y. & Zhao, W. Electroanalysis 19 , 755–768 (2007).

Article   Google Scholar  

Ledesma, H. A. et al. Nature Nanotechnol. 14 , 645–657 (2019).

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Brahlek, M., Koirala, N., Bansal, N. & Oh, S. Solid State Commun. 215–216 , 54–62 (2015).

Choi, Y. & Lee, S. Y. Nature Rev. Chem . https://doi.org/10.1038/s41570-020-00221-w (2020).

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How to Write a Literature Review

What is a literature review.

• What Is the Literature
• Writing the Review

A literature review is much more than an annotated bibliography or a list of separate reviews of articles and books. It is a critical, analytical summary and synthesis of the current knowledge of a topic. Thus it should compare and relate different theories, findings, etc, rather than just summarize them individually. In addition, it should have a particular focus or theme to organize the review. It does not have to be an exhaustive account of everything published on the topic, but it should discuss all the significant academic literature and other relevant sources important for that focus.

This is meant to be a general guide to writing a literature review: ways to structure one, what to include, how it supplements other research. For more specific help on writing a review, and especially for help on finding the literature to review, sign up for a Personal Research Session .

The specific organization of a literature review depends on the type and purpose of the review, as well as on the specific field or topic being reviewed. But in general, it is a relatively brief but thorough exploration of past and current work on a topic. Rather than a chronological listing of previous work, though, literature reviews are usually organized thematically, such as different theoretical approaches, methodologies, or specific issues or concepts involved in the topic. A thematic organization makes it much easier to examine contrasting perspectives, theoretical approaches, methodologies, findings, etc, and to analyze the strengths and weaknesses of, and point out any gaps in, previous research. And this is the heart of what a literature review is about. A literature review may offer new interpretations, theoretical approaches, or other ideas; if it is part of a research proposal or report it should demonstrate the relationship of the proposed or reported research to others' work; but whatever else it does, it must provide a critical overview of the current state of research efforts. 

Literature reviews are common and very important in the sciences and social sciences. They are less common and have a less important role in the humanities, but they do have a place, especially stand-alone reviews.

Types of Literature Reviews

There are different types of literature reviews, and different purposes for writing a review, but the most common are:

• Stand-alone literature review articles . These provide an overview and analysis of the current state of research on a topic or question. The goal is to evaluate and compare previous research on a topic to provide an analysis of what is currently known, and also to reveal controversies, weaknesses, and gaps in current work, thus pointing to directions for future research. You can find examples published in any number of academic journals, but there is a series of Annual Reviews of *Subject* which are specifically devoted to literature review articles. Writing a stand-alone review is often an effective way to get a good handle on a topic and to develop ideas for your own research program. For example, contrasting theoretical approaches or conflicting interpretations of findings can be the basis of your research project: can you find evidence supporting one interpretation against another, or can you propose an alternative interpretation that overcomes their limitations?
• Part of a research proposal . This could be a proposal for a PhD dissertation, a senior thesis, or a class project. It could also be a submission for a grant. The literature review, by pointing out the current issues and questions concerning a topic, is a crucial part of demonstrating how your proposed research will contribute to the field, and thus of convincing your thesis committee to allow you to pursue the topic of your interest or a funding agency to pay for your research efforts.
• Part of a research report . When you finish your research and write your thesis or paper to present your findings, it should include a literature review to provide the context to which your work is a contribution. Your report, in addition to detailing the methods, results, etc. of your research, should show how your work relates to others' work.

A literature review for a research report is often a revision of the review for a research proposal, which can be a revision of a stand-alone review. Each revision should be a fairly extensive revision. With the increased knowledge of and experience in the topic as you proceed, your understanding of the topic will increase. Thus, you will be in a better position to analyze and critique the literature. In addition, your focus will change as you proceed in your research. Some areas of the literature you initially reviewed will be marginal or irrelevant for your eventual research, and you will need to explore other areas more thoroughly. 

Examples of Literature Reviews

See the series of Annual Reviews of *Subject* which are specifically devoted to literature review articles to find many examples of stand-alone literature reviews in the biomedical, physical, and social sciences. 

Research report articles vary in how they are organized, but a common general structure is to have sections such as:

• Abstract - Brief summary of the contents of the article
• Introduction - A explanation of the purpose of the study, a statement of the research question(s) the study intends to address
• Literature review - A critical assessment of the work done so far on this topic, to show how the current study relates to what has already been done
• Methods - How the study was carried out (e.g. instruments or equipment, procedures, methods to gather and analyze data)
• Results - What was found in the course of the study
• Discussion - What do the results mean
• Conclusion - State the conclusions and implications of the results, and discuss how it relates to the work reviewed in the literature review; also, point to directions for further work in the area

Here are some articles that illustrate variations on this theme. There is no need to read the entire articles (unless the contents interest you); just quickly browse through to see the sections, and see how each section is introduced and what is contained in them.

The Determinants of Undergraduate Grade Point Average: The Relative Importance of Family Background, High School Resources, and Peer Group Effects , in The Journal of Human Resources , v. 34 no. 2 (Spring 1999), p. 268-293.

This article has a standard breakdown of sections:

• Introduction
• Literature Review
• Some discussion sections

First Encounters of the Bureaucratic Kind: Early Freshman Experiences with a Campus Bureaucracy , in The Journal of Higher Education , v. 67 no. 6 (Nov-Dec 1996), p. 660-691.

This one does not have a section specifically labeled as a "literature review" or "review of the literature," but the first few sections cite a long list of other sources discussing previous research in the area before the authors present their own study they are reporting.

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A literature review surveys prior research published in books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated. Literature reviews are designed to provide an overview of sources you have used in researching a particular topic and to demonstrate to your readers how your research fits within existing scholarship about the topic.

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . Fourth edition. Thousand Oaks, CA: SAGE, 2014.

Importance of a Good Literature Review

A literature review may consist of simply a summary of key sources, but in the social sciences, a literature review usually has an organizational pattern and combines both summary and synthesis, often within specific conceptual categories . A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information in a way that informs how you are planning to investigate a research problem. The analytical features of a literature review might:

• Give a new interpretation of old material or combine new with old interpretations,
• Trace the intellectual progression of the field, including major debates,
• Depending on the situation, evaluate the sources and advise the reader on the most pertinent or relevant research, or
• Usually in the conclusion of a literature review, identify where gaps exist in how a problem has been researched to date.

Given this, the purpose of a literature review is to:

• Place each work in the context of its contribution to understanding the research problem being studied.
• Describe the relationship of each work to the others under consideration.
• Identify new ways to interpret prior research.
• Reveal any gaps that exist in the literature.
• Resolve conflicts amongst seemingly contradictory previous studies.
• Identify areas of prior scholarship to prevent duplication of effort.
• Point the way in fulfilling a need for additional research.
• Locate your own research within the context of existing literature [very important].

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper. 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . Los Angeles, CA: SAGE, 2011; Knopf, Jeffrey W. "Doing a Literature Review." PS: Political Science and Politics 39 (January 2006): 127-132; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012.

Types of Literature Reviews

It is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the primary studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally among scholars that become part of the body of epistemological traditions within the field.

In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews. Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are a number of approaches you could adopt depending upon the type of analysis underpinning your study.

Argumentative Review This form examines literature selectively in order to support or refute an argument, deeply embedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to make summary claims of the sort found in systematic reviews [see below].

Integrative Review Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses or research problems. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication. This is the most common form of review in the social sciences.

Historical Review Few things rest in isolation from historical precedent. Historical literature reviews focus on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review A review does not always focus on what someone said [findings], but how they came about saying what they say [method of analysis]. Reviewing methods of analysis provides a framework of understanding at different levels [i.e. those of theory, substantive fields, research approaches, and data collection and analysis techniques], how researchers draw upon a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection, and data analysis. This approach helps highlight ethical issues which you should be aware of and consider as you go through your own study.

Systematic Review This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. The goal is to deliberately document, critically evaluate, and summarize scientifically all of the research about a clearly defined research problem . Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?" This type of literature review is primarily applied to examining prior research studies in clinical medicine and allied health fields, but it is increasingly being used in the social sciences.

Theoretical Review The purpose of this form is to examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review helps to establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

NOTE : Most often the literature review will incorporate some combination of types. For example, a review that examines literature supporting or refuting an argument, assumption, or philosophical problem related to the research problem will also need to include writing supported by sources that establish the history of these arguments in the literature.

Baumeister, Roy F. and Mark R. Leary. "Writing Narrative Literature Reviews."  Review of General Psychology 1 (September 1997): 311-320; Mark R. Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Kennedy, Mary M. "Defining a Literature." Educational Researcher 36 (April 2007): 139-147; Petticrew, Mark and Helen Roberts. Systematic Reviews in the Social Sciences: A Practical Guide . Malden, MA: Blackwell Publishers, 2006; Torracro, Richard. "Writing Integrative Literature Reviews: Guidelines and Examples." Human Resource Development Review 4 (September 2005): 356-367; Rocco, Tonette S. and Maria S. Plakhotnik. "Literature Reviews, Conceptual Frameworks, and Theoretical Frameworks: Terms, Functions, and Distinctions." Human Ressource Development Review 8 (March 2008): 120-130; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

Structure and Writing Style

I.  Thinking About Your Literature Review

The structure of a literature review should include the following in support of understanding the research problem :

• An overview of the subject, issue, or theory under consideration, along with the objectives of the literature review,
• Division of works under review into themes or categories [e.g. works that support a particular position, those against, and those offering alternative approaches entirely],
• An explanation of how each work is similar to and how it varies from the others,
• Conclusions as to which pieces are best considered in their argument, are most convincing of their opinions, and make the greatest contribution to the understanding and development of their area of research.

The critical evaluation of each work should consider :

• Provenance -- what are the author's credentials? Are the author's arguments supported by evidence [e.g. primary historical material, case studies, narratives, statistics, recent scientific findings]?
• Methodology -- were the techniques used to identify, gather, and analyze the data appropriate to addressing the research problem? Was the sample size appropriate? Were the results effectively interpreted and reported?
• Objectivity -- is the author's perspective even-handed or prejudicial? Is contrary data considered or is certain pertinent information ignored to prove the author's point?
• Persuasiveness -- which of the author's theses are most convincing or least convincing?
• Validity -- are the author's arguments and conclusions convincing? Does the work ultimately contribute in any significant way to an understanding of the subject?

II.  Development of the Literature Review

Four Basic Stages of Writing 1.  Problem formulation -- which topic or field is being examined and what are its component issues? 2.  Literature search -- finding materials relevant to the subject being explored. 3.  Data evaluation -- determining which literature makes a significant contribution to the understanding of the topic. 4.  Analysis and interpretation -- discussing the findings and conclusions of pertinent literature.

Consider the following issues before writing the literature review: Clarify If your assignment is not specific about what form your literature review should take, seek clarification from your professor by asking these questions: 1.  Roughly how many sources would be appropriate to include? 2.  What types of sources should I review (books, journal articles, websites; scholarly versus popular sources)? 3.  Should I summarize, synthesize, or critique sources by discussing a common theme or issue? 4.  Should I evaluate the sources in any way beyond evaluating how they relate to understanding the research problem? 5.  Should I provide subheadings and other background information, such as definitions and/or a history? Find Models Use the exercise of reviewing the literature to examine how authors in your discipline or area of interest have composed their literature review sections. Read them to get a sense of the types of themes you might want to look for in your own research or to identify ways to organize your final review. The bibliography or reference section of sources you've already read, such as required readings in the course syllabus, are also excellent entry points into your own research. Narrow the Topic The narrower your topic, the easier it will be to limit the number of sources you need to read in order to obtain a good survey of relevant resources. Your professor will probably not expect you to read everything that's available about the topic, but you'll make the act of reviewing easier if you first limit scope of the research problem. A good strategy is to begin by searching the USC Libraries Catalog for recent books about the topic and review the table of contents for chapters that focuses on specific issues. You can also review the indexes of books to find references to specific issues that can serve as the focus of your research. For example, a book surveying the history of the Israeli-Palestinian conflict may include a chapter on the role Egypt has played in mediating the conflict, or look in the index for the pages where Egypt is mentioned in the text. Consider Whether Your Sources are Current Some disciplines require that you use information that is as current as possible. This is particularly true in disciplines in medicine and the sciences where research conducted becomes obsolete very quickly as new discoveries are made. However, when writing a review in the social sciences, a survey of the history of the literature may be required. In other words, a complete understanding the research problem requires you to deliberately examine how knowledge and perspectives have changed over time. Sort through other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to explore what is considered by scholars to be a "hot topic" and what is not.

III.  Ways to Organize Your Literature Review

Chronology of Events If your review follows the chronological method, you could write about the materials according to when they were published. This approach should only be followed if a clear path of research building on previous research can be identified and that these trends follow a clear chronological order of development. For example, a literature review that focuses on continuing research about the emergence of German economic power after the fall of the Soviet Union. By Publication Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on environmental studies of brown fields if the progression revealed, for example, a change in the soil collection practices of the researchers who wrote and/or conducted the studies. Thematic [“conceptual categories”] A thematic literature review is the most common approach to summarizing prior research in the social and behavioral sciences. Thematic reviews are organized around a topic or issue, rather than the progression of time, although the progression of time may still be incorporated into a thematic review. For example, a review of the Internet’s impact on American presidential politics could focus on the development of online political satire. While the study focuses on one topic, the Internet’s impact on American presidential politics, it would still be organized chronologically reflecting technological developments in media. The difference in this example between a "chronological" and a "thematic" approach is what is emphasized the most: themes related to the role of the Internet in presidential politics. Note that more authentic thematic reviews tend to break away from chronological order. A review organized in this manner would shift between time periods within each section according to the point being made. Methodological A methodological approach focuses on the methods utilized by the researcher. For the Internet in American presidential politics project, one methodological approach would be to look at cultural differences between the portrayal of American presidents on American, British, and French websites. Or the review might focus on the fundraising impact of the Internet on a particular political party. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed.

Other Sections of Your Literature Review Once you've decided on the organizational method for your literature review, the sections you need to include in the paper should be easy to figure out because they arise from your organizational strategy. In other words, a chronological review would have subsections for each vital time period; a thematic review would have subtopics based upon factors that relate to the theme or issue. However, sometimes you may need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. However, only include what is necessary for the reader to locate your study within the larger scholarship about the research problem.

Here are examples of other sections, usually in the form of a single paragraph, you may need to include depending on the type of review you write:

• Current Situation : Information necessary to understand the current topic or focus of the literature review.
• Sources Used : Describes the methods and resources [e.g., databases] you used to identify the literature you reviewed.
• History : The chronological progression of the field, the research literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Selection Methods : Criteria you used to select (and perhaps exclude) sources in your literature review. For instance, you might explain that your review includes only peer-reviewed [i.e., scholarly] sources.
• Standards : Description of the way in which you present your information.
• Questions for Further Research : What questions about the field has the review sparked? How will you further your research as a result of the review?

IV.  Writing Your Literature Review

Once you've settled on how to organize your literature review, you're ready to write each section. When writing your review, keep in mind these issues.

Use Evidence A literature review section is, in this sense, just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence [citations] that demonstrates that what you are saying is valid. Be Selective Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the research problem, whether it is thematic, methodological, or chronological. Related items that provide additional information, but that are not key to understanding the research problem, can be included in a list of further readings . Use Quotes Sparingly Some short quotes are appropriate if you want to emphasize a point, or if what an author stated cannot be easily paraphrased. Sometimes you may need to quote certain terminology that was coined by the author, is not common knowledge, or taken directly from the study. Do not use extensive quotes as a substitute for using your own words in reviewing the literature. Summarize and Synthesize Remember to summarize and synthesize your sources within each thematic paragraph as well as throughout the review. Recapitulate important features of a research study, but then synthesize it by rephrasing the study's significance and relating it to your own work and the work of others. Keep Your Own Voice While the literature review presents others' ideas, your voice [the writer's] should remain front and center. For example, weave references to other sources into what you are writing but maintain your own voice by starting and ending the paragraph with your own ideas and wording. Use Caution When Paraphrasing When paraphrasing a source that is not your own, be sure to represent the author's information or opinions accurately and in your own words. Even when paraphrasing an author’s work, you still must provide a citation to that work.

V.  Common Mistakes to Avoid

These are the most common mistakes made in reviewing social science research literature.

• Sources in your literature review do not clearly relate to the research problem;
• You do not take sufficient time to define and identify the most relevant sources to use in the literature review related to the research problem;
• Relies exclusively on secondary analytical sources rather than including relevant primary research studies or data;
• Uncritically accepts another researcher's findings and interpretations as valid, rather than examining critically all aspects of the research design and analysis;
• Does not describe the search procedures that were used in identifying the literature to review;
• Reports isolated statistical results rather than synthesizing them in chi-squared or meta-analytic methods; and,
• Only includes research that validates assumptions and does not consider contrary findings and alternative interpretations found in the literature.

Cook, Kathleen E. and Elise Murowchick. “Do Literature Review Skills Transfer from One Course to Another?” Psychology Learning and Teaching 13 (March 2014): 3-11; Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . London: SAGE, 2011; Literature Review Handout. Online Writing Center. Liberty University; Literature Reviews. The Writing Center. University of North Carolina; Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: SAGE, 2016; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012; Randolph, Justus J. “A Guide to Writing the Dissertation Literature Review." Practical Assessment, Research, and Evaluation. vol. 14, June 2009; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016; Taylor, Dena. The Literature Review: A Few Tips On Conducting It. University College Writing Centre. University of Toronto; Writing a Literature Review. Academic Skills Centre. University of Canberra.

Writing Tip

Break Out of Your Disciplinary Box!

Thinking interdisciplinarily about a research problem can be a rewarding exercise in applying new ideas, theories, or concepts to an old problem. For example, what might cultural anthropologists say about the continuing conflict in the Middle East? In what ways might geographers view the need for better distribution of social service agencies in large cities than how social workers might study the issue? You don’t want to substitute a thorough review of core research literature in your discipline for studies conducted in other fields of study. However, particularly in the social sciences, thinking about research problems from multiple vectors is a key strategy for finding new solutions to a problem or gaining a new perspective. Consult with a librarian about identifying research databases in other disciplines; almost every field of study has at least one comprehensive database devoted to indexing its research literature.

Frodeman, Robert. The Oxford Handbook of Interdisciplinarity . New York: Oxford University Press, 2010.

Another Writing Tip

Don't Just Review for Content!

While conducting a review of the literature, maximize the time you devote to writing this part of your paper by thinking broadly about what you should be looking for and evaluating. Review not just what scholars are saying, but how are they saying it. Some questions to ask:

• How are they organizing their ideas?
• What methods have they used to study the problem?
• What theories have been used to explain, predict, or understand their research problem?
• What sources have they cited to support their conclusions?
• How have they used non-textual elements [e.g., charts, graphs, figures, etc.] to illustrate key points?

When you begin to write your literature review section, you'll be glad you dug deeper into how the research was designed and constructed because it establishes a means for developing more substantial analysis and interpretation of the research problem.

Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1 998.

Yet Another Writing Tip

When Do I Know I Can Stop Looking and Move On?

Here are several strategies you can utilize to assess whether you've thoroughly reviewed the literature:

• Look for repeating patterns in the research findings . If the same thing is being said, just by different people, then this likely demonstrates that the research problem has hit a conceptual dead end. At this point consider: Does your study extend current research?  Does it forge a new path? Or, does is merely add more of the same thing being said?
• Look at sources the authors cite to in their work . If you begin to see the same researchers cited again and again, then this is often an indication that no new ideas have been generated to address the research problem.
• Search Google Scholar to identify who has subsequently cited leading scholars already identified in your literature review [see next sub-tab]. This is called citation tracking and there are a number of sources that can help you identify who has cited whom, particularly scholars from outside of your discipline. Here again, if the same authors are being cited again and again, this may indicate no new literature has been written on the topic.

Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: Sage, 2016; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

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Literature Reviews

What this handout is about.

This handout will explain what literature reviews are and offer insights into the form and construction of literature reviews in the humanities, social sciences, and sciences.

Introduction

OK. You’ve got to write a literature review. You dust off a novel and a book of poetry, settle down in your chair, and get ready to issue a “thumbs up” or “thumbs down” as you leaf through the pages. “Literature review” done. Right?

Wrong! The “literature” of a literature review refers to any collection of materials on a topic, not necessarily the great literary texts of the world. “Literature” could be anything from a set of government pamphlets on British colonial methods in Africa to scholarly articles on the treatment of a torn ACL. And a review does not necessarily mean that your reader wants you to give your personal opinion on whether or not you liked these sources.

What is a literature review, then?

A literature review discusses published information in a particular subject area, and sometimes information in a particular subject area within a certain time period.

A literature review can be just a simple summary of the sources, but it usually has an organizational pattern and combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

But how is a literature review different from an academic research paper?

The main focus of an academic research paper is to develop a new argument, and a research paper is likely to contain a literature review as one of its parts. In a research paper, you use the literature as a foundation and as support for a new insight that you contribute. The focus of a literature review, however, is to summarize and synthesize the arguments and ideas of others without adding new contributions.

Why do we write literature reviews?

Literature reviews provide you with a handy guide to a particular topic. If you have limited time to conduct research, literature reviews can give you an overview or act as a stepping stone. For professionals, they are useful reports that keep them up to date with what is current in the field. For scholars, the depth and breadth of the literature review emphasizes the credibility of the writer in his or her field. Literature reviews also provide a solid background for a research paper’s investigation. Comprehensive knowledge of the literature of the field is essential to most research papers.

Who writes these things, anyway?

Literature reviews are written occasionally in the humanities, but mostly in the sciences and social sciences; in experiment and lab reports, they constitute a section of the paper. Sometimes a literature review is written as a paper in itself.

Let’s get to it! What should I do before writing the literature review?

If your assignment is not very specific, seek clarification from your instructor:

• Roughly how many sources should you include?
• What types of sources (books, journal articles, websites)?
• Should you summarize, synthesize, or critique your sources by discussing a common theme or issue?
• Should you evaluate your sources?
• Should you provide subheadings and other background information, such as definitions and/or a history?

Find models

Look for other literature reviews in your area of interest or in the discipline and read them to get a sense of the types of themes you might want to look for in your own research or ways to organize your final review. You can simply put the word “review” in your search engine along with your other topic terms to find articles of this type on the Internet or in an electronic database. The bibliography or reference section of sources you’ve already read are also excellent entry points into your own research.

Narrow your topic

There are hundreds or even thousands of articles and books on most areas of study. The narrower your topic, the easier it will be to limit the number of sources you need to read in order to get a good survey of the material. Your instructor will probably not expect you to read everything that’s out there on the topic, but you’ll make your job easier if you first limit your scope.

Keep in mind that UNC Libraries have research guides and to databases relevant to many fields of study. You can reach out to the subject librarian for a consultation: https://library.unc.edu/support/consultations/ .

And don’t forget to tap into your professor’s (or other professors’) knowledge in the field. Ask your professor questions such as: “If you had to read only one book from the 90’s on topic X, what would it be?” Questions such as this help you to find and determine quickly the most seminal pieces in the field.

Consider whether your sources are current

Some disciplines require that you use information that is as current as possible. In the sciences, for instance, treatments for medical problems are constantly changing according to the latest studies. Information even two years old could be obsolete. However, if you are writing a review in the humanities, history, or social sciences, a survey of the history of the literature may be what is needed, because what is important is how perspectives have changed through the years or within a certain time period. Try sorting through some other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to consider what is currently of interest to scholars in this field and what is not.

Strategies for writing the literature review

Find a focus.

A literature review, like a term paper, is usually organized around ideas, not the sources themselves as an annotated bibliography would be organized. This means that you will not just simply list your sources and go into detail about each one of them, one at a time. No. As you read widely but selectively in your topic area, consider instead what themes or issues connect your sources together. Do they present one or different solutions? Is there an aspect of the field that is missing? How well do they present the material and do they portray it according to an appropriate theory? Do they reveal a trend in the field? A raging debate? Pick one of these themes to focus the organization of your review.

Convey it to your reader

A literature review may not have a traditional thesis statement (one that makes an argument), but you do need to tell readers what to expect. Try writing a simple statement that lets the reader know what is your main organizing principle. Here are a couple of examples:

The current trend in treatment for congestive heart failure combines surgery and medicine. More and more cultural studies scholars are accepting popular media as a subject worthy of academic consideration.

Consider organization

You’ve got a focus, and you’ve stated it clearly and directly. Now what is the most effective way of presenting the information? What are the most important topics, subtopics, etc., that your review needs to include? And in what order should you present them? Develop an organization for your review at both a global and local level:

First, cover the basic categories

Just like most academic papers, literature reviews also must contain at least three basic elements: an introduction or background information section; the body of the review containing the discussion of sources; and, finally, a conclusion and/or recommendations section to end the paper. The following provides a brief description of the content of each:

• Introduction: Gives a quick idea of the topic of the literature review, such as the central theme or organizational pattern.
• Body: Contains your discussion of sources and is organized either chronologically, thematically, or methodologically (see below for more information on each).
• Conclusions/Recommendations: Discuss what you have drawn from reviewing literature so far. Where might the discussion proceed?

Organizing the body

Once you have the basic categories in place, then you must consider how you will present the sources themselves within the body of your paper. Create an organizational method to focus this section even further.

To help you come up with an overall organizational framework for your review, consider the following scenario:

You’ve decided to focus your literature review on materials dealing with sperm whales. This is because you’ve just finished reading Moby Dick, and you wonder if that whale’s portrayal is really real. You start with some articles about the physiology of sperm whales in biology journals written in the 1980’s. But these articles refer to some British biological studies performed on whales in the early 18th century. So you check those out. Then you look up a book written in 1968 with information on how sperm whales have been portrayed in other forms of art, such as in Alaskan poetry, in French painting, or on whale bone, as the whale hunters in the late 19th century used to do. This makes you wonder about American whaling methods during the time portrayed in Moby Dick, so you find some academic articles published in the last five years on how accurately Herman Melville portrayed the whaling scene in his novel.

Now consider some typical ways of organizing the sources into a review:

• Chronological: If your review follows the chronological method, you could write about the materials above according to when they were published. For instance, first you would talk about the British biological studies of the 18th century, then about Moby Dick, published in 1851, then the book on sperm whales in other art (1968), and finally the biology articles (1980s) and the recent articles on American whaling of the 19th century. But there is relatively no continuity among subjects here. And notice that even though the sources on sperm whales in other art and on American whaling are written recently, they are about other subjects/objects that were created much earlier. Thus, the review loses its chronological focus.
• By publication: Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on biological studies of sperm whales if the progression revealed a change in dissection practices of the researchers who wrote and/or conducted the studies.
• By trend: A better way to organize the above sources chronologically is to examine the sources under another trend, such as the history of whaling. Then your review would have subsections according to eras within this period. For instance, the review might examine whaling from pre-1600-1699, 1700-1799, and 1800-1899. Under this method, you would combine the recent studies on American whaling in the 19th century with Moby Dick itself in the 1800-1899 category, even though the authors wrote a century apart.
• Thematic: Thematic reviews of literature are organized around a topic or issue, rather than the progression of time. However, progression of time may still be an important factor in a thematic review. For instance, the sperm whale review could focus on the development of the harpoon for whale hunting. While the study focuses on one topic, harpoon technology, it will still be organized chronologically. The only difference here between a “chronological” and a “thematic” approach is what is emphasized the most: the development of the harpoon or the harpoon technology.But more authentic thematic reviews tend to break away from chronological order. For instance, a thematic review of material on sperm whales might examine how they are portrayed as “evil” in cultural documents. The subsections might include how they are personified, how their proportions are exaggerated, and their behaviors misunderstood. A review organized in this manner would shift between time periods within each section according to the point made.
• Methodological: A methodological approach differs from the two above in that the focusing factor usually does not have to do with the content of the material. Instead, it focuses on the “methods” of the researcher or writer. For the sperm whale project, one methodological approach would be to look at cultural differences between the portrayal of whales in American, British, and French art work. Or the review might focus on the economic impact of whaling on a community. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed. Once you’ve decided on the organizational method for the body of the review, the sections you need to include in the paper should be easy to figure out. They should arise out of your organizational strategy. In other words, a chronological review would have subsections for each vital time period. A thematic review would have subtopics based upon factors that relate to the theme or issue.

Sometimes, though, you might need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. Put in only what is necessary. Here are a few other sections you might want to consider:

• Current Situation: Information necessary to understand the topic or focus of the literature review.
• History: The chronological progression of the field, the literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Methods and/or Standards: The criteria you used to select the sources in your literature review or the way in which you present your information. For instance, you might explain that your review includes only peer-reviewed articles and journals.

Questions for Further Research: What questions about the field has the review sparked? How will you further your research as a result of the review?

Begin composing

Once you’ve settled on a general pattern of organization, you’re ready to write each section. There are a few guidelines you should follow during the writing stage as well. Here is a sample paragraph from a literature review about sexism and language to illuminate the following discussion:

However, other studies have shown that even gender-neutral antecedents are more likely to produce masculine images than feminine ones (Gastil, 1990). Hamilton (1988) asked students to complete sentences that required them to fill in pronouns that agreed with gender-neutral antecedents such as “writer,” “pedestrian,” and “persons.” The students were asked to describe any image they had when writing the sentence. Hamilton found that people imagined 3.3 men to each woman in the masculine “generic” condition and 1.5 men per woman in the unbiased condition. Thus, while ambient sexism accounted for some of the masculine bias, sexist language amplified the effect. (Source: Erika Falk and Jordan Mills, “Why Sexist Language Affects Persuasion: The Role of Homophily, Intended Audience, and Offense,” Women and Language19:2).

Use evidence

In the example above, the writers refer to several other sources when making their point. A literature review in this sense is just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence to show that what you are saying is valid.

Be selective

Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the review’s focus, whether it is thematic, methodological, or chronological.

Use quotes sparingly

Falk and Mills do not use any direct quotes. That is because the survey nature of the literature review does not allow for in-depth discussion or detailed quotes from the text. Some short quotes here and there are okay, though, if you want to emphasize a point, or if what the author said just cannot be rewritten in your own words. Notice that Falk and Mills do quote certain terms that were coined by the author, not common knowledge, or taken directly from the study. But if you find yourself wanting to put in more quotes, check with your instructor.

Summarize and synthesize

Remember to summarize and synthesize your sources within each paragraph as well as throughout the review. The authors here recapitulate important features of Hamilton’s study, but then synthesize it by rephrasing the study’s significance and relating it to their own work.

Keep your own voice

While the literature review presents others’ ideas, your voice (the writer’s) should remain front and center. Notice that Falk and Mills weave references to other sources into their own text, but they still maintain their own voice by starting and ending the paragraph with their own ideas and their own words. The sources support what Falk and Mills are saying.

Use caution when paraphrasing

When paraphrasing a source that is not your own, be sure to represent the author’s information or opinions accurately and in your own words. In the preceding example, Falk and Mills either directly refer in the text to the author of their source, such as Hamilton, or they provide ample notation in the text when the ideas they are mentioning are not their own, for example, Gastil’s. For more information, please see our handout on plagiarism .

Revise, revise, revise

Draft in hand? Now you’re ready to revise. Spending a lot of time revising is a wise idea, because your main objective is to present the material, not the argument. So check over your review again to make sure it follows the assignment and/or your outline. Then, just as you would for most other academic forms of writing, rewrite or rework the language of your review so that you’ve presented your information in the most concise manner possible. Be sure to use terminology familiar to your audience; get rid of unnecessary jargon or slang. Finally, double check that you’ve documented your sources and formatted the review appropriately for your discipline. For tips on the revising and editing process, see our handout on revising drafts .

Works consulted

We consulted these works while writing this handout. This is not a comprehensive list of resources on the handout’s topic, and we encourage you to do your own research to find additional publications. Please do not use this list as a model for the format of your own reference list, as it may not match the citation style you are using. For guidance on formatting citations, please see the UNC Libraries citation tutorial . We revise these tips periodically and welcome feedback.

Anson, Chris M., and Robert A. Schwegler. 2010. The Longman Handbook for Writers and Readers , 6th ed. New York: Longman.

Jones, Robert, Patrick Bizzaro, and Cynthia Selfe. 1997. The Harcourt Brace Guide to Writing in the Disciplines . New York: Harcourt Brace.

Lamb, Sandra E. 1998. How to Write It: A Complete Guide to Everything You’ll Ever Write . Berkeley: Ten Speed Press.

Rosen, Leonard J., and Laurence Behrens. 2003. The Allyn & Bacon Handbook , 5th ed. New York: Longman.

Troyka, Lynn Quittman, and Doug Hesse. 2016. Simon and Schuster Handbook for Writers , 11th ed. London: Pearson.

You may reproduce it for non-commercial use if you use the entire handout and attribute the source: The Writing Center, University of North Carolina at Chapel Hill

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Literature Reviews

• What is a literature review?
• Steps in the Literature Review Process
• Define your research question
• Determine inclusion and exclusion criteria
• Choose databases and search
• Review Results
• Synthesize Results
• Analyze Results
• Librarian Support

What is a Literature Review?

A literature or narrative review is a comprehensive review and analysis of the published literature on a specific topic or research question. The literature that is reviewed contains: books, articles, academic articles, conference proceedings, association papers, and dissertations. It contains the most pertinent studies and points to important past and current research and practices. It provides background and context, and shows how your research will contribute to the field. 

A literature review should: 

• Provide a comprehensive and updated review of the literature;
• Explain why this review has taken place;
• Articulate a position or hypothesis;
• Acknowledge and account for conflicting and corroborating points of view

From  S age Research Methods

Purpose of a Literature Review

A literature review can be written as an introduction to a study to:

• Demonstrate how a study fills a gap in research
• Compare a study with other research that's been done

Or it can be a separate work (a research article on its own) which:

• Organizes or describes a topic
• Describes variables within a particular issue/problem

Limitations of a Literature Review

Some of the limitations of a literature review are:

• It's a snapshot in time. Unlike other reviews, this one has beginning, a middle and an end. There may be future developments that could make your work less relevant.
• It may be too focused. Some niche studies may miss the bigger picture.
• It can be difficult to be comprehensive. There is no way to make sure all the literature on a topic was considered.
• It is easy to be biased if you stick to top tier journals. There may be other places where people are publishing exemplary research. Look to open access publications and conferences to reflect a more inclusive collection. Also, make sure to include opposing views (and not just supporting evidence).

Source: Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal, vol. 26, no. 2, June 2009, pp. 91–108. Wiley Online Library, doi:10.1111/j.1471-1842.2009.00848.x.

Meryl Brodsky : Communication and Information Studies

Hannah Chapman Tripp : Biology, Neuroscience

Carolyn Cunningham : Human Development & Family Sciences, Psychology, Sociology

Larayne Dallas : Engineering

Janelle Hedstrom : Special Education, Curriculum & Instruction, Ed Leadership & Policy ​

Susan Macicak : Linguistics

Imelda Vetter : Dell Medical School

For help in other subject areas, please see the guide to library specialists by subject .

Periodically, UT Libraries runs a workshop covering the basics and library support for literature reviews. While we try to offer these once per academic year, we find providing the recording to be helpful to community members who have missed the session. Following is the most recent recording of the workshop, Conducting a Literature Review. To view the recording, a UT login is required.

• October 26, 2022 recording
• Last Updated: Oct 26, 2022 2:49 PM
• URL: https://guides.lib.utexas.edu/literaturereviews

What Is A Literature Review?

A plain-language explainer (with examples).

By:  Derek Jansen (MBA) & Kerryn Warren (PhD) | June 2020 (Updated May 2023)

If you’re faced with writing a dissertation or thesis, chances are you’ve encountered the term “literature review” . If you’re on this page, you’re probably not 100% what the literature review is all about. The good news is that you’ve come to the right place.

Literature Review 101

• What (exactly) is a literature review
• What’s the purpose of the literature review chapter
• How to find high-quality resources
• How to structure your literature review chapter
• Example of an actual literature review

What is a literature review?

The word “literature review” can refer to two related things that are part of the broader literature review process. The first is the task of  reviewing the literature  – i.e. sourcing and reading through the existing research relating to your research topic. The second is the  actual chapter  that you write up in your dissertation, thesis or research project. Let’s look at each of them:

Reviewing the literature

The first step of any literature review is to hunt down and  read through the existing research  that’s relevant to your research topic. To do this, you’ll use a combination of tools (we’ll discuss some of these later) to find journal articles, books, ebooks, research reports, dissertations, theses and any other credible sources of information that relate to your topic. You’ll then  summarise and catalogue these  for easy reference when you write up your literature review chapter. 

The literature review chapter

The second step of the literature review is to write the actual literature review chapter (this is usually the second chapter in a typical dissertation or thesis structure ). At the simplest level, the literature review chapter is an  overview of the key literature  that’s relevant to your research topic. This chapter should provide a smooth-flowing discussion of what research has already been done, what is known, what is unknown and what is contested in relation to your research topic. So, you can think of it as an  integrated review of the state of knowledge  around your research topic. 

What’s the purpose of a literature review?

The literature review chapter has a few important functions within your dissertation, thesis or research project. Let’s take a look at these:

Purpose #1 – Demonstrate your topic knowledge

The first function of the literature review chapter is, quite simply, to show the reader (or marker) that you  know what you’re talking about . In other words, a good literature review chapter demonstrates that you’ve read the relevant existing research and understand what’s going on – who’s said what, what’s agreed upon, disagreed upon and so on. This needs to be  more than just a summary  of who said what – it needs to integrate the existing research to  show how it all fits together  and what’s missing (which leads us to purpose #2, next). 

Purpose #2 – Reveal the research gap that you’ll fill

The second function of the literature review chapter is to  show what’s currently missing  from the existing research, to lay the foundation for your own research topic. In other words, your literature review chapter needs to show that there are currently “missing pieces” in terms of the bigger puzzle, and that  your study will fill one of those research gaps . By doing this, you are showing that your research topic is original and will help contribute to the body of knowledge. In other words, the literature review helps justify your research topic.  

Purpose #3 – Lay the foundation for your conceptual framework

The third function of the literature review is to form the  basis for a conceptual framework . Not every research topic will necessarily have a conceptual framework, but if your topic does require one, it needs to be rooted in your literature review. 

For example, let’s say your research aims to identify the drivers of a certain outcome – the factors which contribute to burnout in office workers. In this case, you’d likely develop a conceptual framework which details the potential factors (e.g. long hours, excessive stress, etc), as well as the outcome (burnout). Those factors would need to emerge from the literature review chapter – they can’t just come from your gut! 

So, in this case, the literature review chapter would uncover each of the potential factors (based on previous studies about burnout), which would then be modelled into a framework. 

Purpose #4 – To inform your methodology

The fourth function of the literature review is to  inform the choice of methodology  for your own research. As we’ve  discussed on the Grad Coach blog , your choice of methodology will be heavily influenced by your research aims, objectives and questions . Given that you’ll be reviewing studies covering a topic close to yours, it makes sense that you could learn a lot from their (well-considered) methodologies.

So, when you’re reviewing the literature, you’ll need to  pay close attention to the research design , methodology and methods used in similar studies, and use these to inform your methodology. Quite often, you’ll be able to  “borrow” from previous studies . This is especially true for quantitative studies , as you can use previously tried and tested measures and scales. 

How do I find articles for my literature review?

Finding quality journal articles is essential to crafting a rock-solid literature review. As you probably already know, not all research is created equally, and so you need to make sure that your literature review is  built on credible research . 

We could write an entire post on how to find quality literature (actually, we have ), but a good starting point is Google Scholar . Google Scholar is essentially the academic equivalent of Google, using Google’s powerful search capabilities to find relevant journal articles and reports. It certainly doesn’t cover every possible resource, but it’s a very useful way to get started on your literature review journey, as it will very quickly give you a good indication of what the  most popular pieces of research  are in your field.

One downside of Google Scholar is that it’s merely a search engine – that is, it lists the articles, but oftentimes  it doesn’t host the articles . So you’ll often hit a paywall when clicking through to journal websites. 

Thankfully, your university should provide you with access to their library, so you can find the article titles using Google Scholar and then search for them by name in your university’s online library. Your university may also provide you with access to  ResearchGate , which is another great source for existing research. 

Remember, the correct search keywords will be super important to get the right information from the start. So, pay close attention to the keywords used in the journal articles you read and use those keywords to search for more articles. If you can’t find a spoon in the kitchen, you haven’t looked in the right drawer. 

Need a helping hand?

How should I structure my literature review?

Unfortunately, there’s no generic universal answer for this one. The structure of your literature review will depend largely on your topic area and your research aims and objectives.

You could potentially structure your literature review chapter according to theme, group, variables , chronologically or per concepts in your field of research. We explain the main approaches to structuring your literature review here . You can also download a copy of our free literature review template to help you establish an initial structure.

In general, it’s also a good idea to start wide (i.e. the big-picture-level) and then narrow down, ending your literature review close to your research questions . However, there’s no universal one “right way” to structure your literature review. The most important thing is not to discuss your sources one after the other like a list – as we touched on earlier, your literature review needs to synthesise the research , not summarise it .

Ultimately, you need to craft your literature review so that it conveys the most important information effectively – it needs to tell a logical story in a digestible way. It’s no use starting off with highly technical terms and then only explaining what these terms mean later. Always assume your reader is not a subject matter expert and hold their hand through a journe y of the literature while keeping the functions of the literature review chapter (which we discussed earlier) front of mind.

Example of a literature review

In the video below, we walk you through a high-quality literature review from a dissertation that earned full distinction. This will give you a clearer view of what a strong literature review looks like in practice and hopefully provide some inspiration for your own. 

Wrapping Up

In this post, we’ve (hopefully) answered the question, “ what is a literature review? “. We’ve also considered the purpose and functions of the literature review, as well as how to find literature and how to structure the literature review chapter. If you’re keen to learn more, check out the literature review section of the Grad Coach blog , as well as our detailed video post covering how to write a literature review . 

Psst… there’s more!

This post is an extract from our bestselling short course, Literature Review Bootcamp . If you want to work smart, you don't want to miss this .

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16 Comments

Thanks for this review. It narrates what’s not been taught as tutors are always in a early to finish their classes.

Thanks for the kind words, Becky. Good luck with your literature review 🙂

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Timothy T. Chol [email protected]

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Great Brief Explanation, thanks

So helpful to me as a student

GradCoach is a fantastic site with brilliant and modern minds behind it.. I spent weeks decoding the substantial academic Jargon and grounding my initial steps on the research process, which could be shortened to a couple of days through the Gradcoach. Thanks again!

This is an amazing talk. I paved way for myself as a researcher. Thank you GradCoach!

Well-presented overview of the literature!

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Ten Simple Rules for Writing a Literature Review

Marco pautasso.

1 Centre for Functional and Evolutionary Ecology (CEFE), CNRS, Montpellier, France

2 Centre for Biodiversity Synthesis and Analysis (CESAB), FRB, Aix-en-Provence, France

Literature reviews are in great demand in most scientific fields. Their need stems from the ever-increasing output of scientific publications [1] . For example, compared to 1991, in 2008 three, eight, and forty times more papers were indexed in Web of Science on malaria, obesity, and biodiversity, respectively [2] . Given such mountains of papers, scientists cannot be expected to examine in detail every single new paper relevant to their interests [3] . Thus, it is both advantageous and necessary to rely on regular summaries of the recent literature. Although recognition for scientists mainly comes from primary research, timely literature reviews can lead to new synthetic insights and are often widely read [4] . For such summaries to be useful, however, they need to be compiled in a professional way [5] .

When starting from scratch, reviewing the literature can require a titanic amount of work. That is why researchers who have spent their career working on a certain research issue are in a perfect position to review that literature. Some graduate schools are now offering courses in reviewing the literature, given that most research students start their project by producing an overview of what has already been done on their research issue [6] . However, it is likely that most scientists have not thought in detail about how to approach and carry out a literature review.

Reviewing the literature requires the ability to juggle multiple tasks, from finding and evaluating relevant material to synthesising information from various sources, from critical thinking to paraphrasing, evaluating, and citation skills [7] . In this contribution, I share ten simple rules I learned working on about 25 literature reviews as a PhD and postdoctoral student. Ideas and insights also come from discussions with coauthors and colleagues, as well as feedback from reviewers and editors.

Rule 1: Define a Topic and Audience

How to choose which topic to review? There are so many issues in contemporary science that you could spend a lifetime of attending conferences and reading the literature just pondering what to review. On the one hand, if you take several years to choose, several other people may have had the same idea in the meantime. On the other hand, only a well-considered topic is likely to lead to a brilliant literature review [8] . The topic must at least be:

• interesting to you (ideally, you should have come across a series of recent papers related to your line of work that call for a critical summary),
• an important aspect of the field (so that many readers will be interested in the review and there will be enough material to write it), and
• a well-defined issue (otherwise you could potentially include thousands of publications, which would make the review unhelpful).

Ideas for potential reviews may come from papers providing lists of key research questions to be answered [9] , but also from serendipitous moments during desultory reading and discussions. In addition to choosing your topic, you should also select a target audience. In many cases, the topic (e.g., web services in computational biology) will automatically define an audience (e.g., computational biologists), but that same topic may also be of interest to neighbouring fields (e.g., computer science, biology, etc.).

Rule 2: Search and Re-search the Literature

After having chosen your topic and audience, start by checking the literature and downloading relevant papers. Five pieces of advice here:

• keep track of the search items you use (so that your search can be replicated [10] ),
• keep a list of papers whose pdfs you cannot access immediately (so as to retrieve them later with alternative strategies),
• use a paper management system (e.g., Mendeley, Papers, Qiqqa, Sente),
• define early in the process some criteria for exclusion of irrelevant papers (these criteria can then be described in the review to help define its scope), and
• do not just look for research papers in the area you wish to review, but also seek previous reviews.

The chances are high that someone will already have published a literature review ( Figure 1 ), if not exactly on the issue you are planning to tackle, at least on a related topic. If there are already a few or several reviews of the literature on your issue, my advice is not to give up, but to carry on with your own literature review,

The bottom-right situation (many literature reviews but few research papers) is not just a theoretical situation; it applies, for example, to the study of the impacts of climate change on plant diseases, where there appear to be more literature reviews than research studies [33] .

• discussing in your review the approaches, limitations, and conclusions of past reviews,
• trying to find a new angle that has not been covered adequately in the previous reviews, and
• incorporating new material that has inevitably accumulated since their appearance.

When searching the literature for pertinent papers and reviews, the usual rules apply:

• be thorough,
• use different keywords and database sources (e.g., DBLP, Google Scholar, ISI Proceedings, JSTOR Search, Medline, Scopus, Web of Science), and
• look at who has cited past relevant papers and book chapters.

Rule 3: Take Notes While Reading

If you read the papers first, and only afterwards start writing the review, you will need a very good memory to remember who wrote what, and what your impressions and associations were while reading each single paper. My advice is, while reading, to start writing down interesting pieces of information, insights about how to organize the review, and thoughts on what to write. This way, by the time you have read the literature you selected, you will already have a rough draft of the review.

Of course, this draft will still need much rewriting, restructuring, and rethinking to obtain a text with a coherent argument [11] , but you will have avoided the danger posed by staring at a blank document. Be careful when taking notes to use quotation marks if you are provisionally copying verbatim from the literature. It is advisable then to reformulate such quotes with your own words in the final draft. It is important to be careful in noting the references already at this stage, so as to avoid misattributions. Using referencing software from the very beginning of your endeavour will save you time.

Rule 4: Choose the Type of Review You Wish to Write

After having taken notes while reading the literature, you will have a rough idea of the amount of material available for the review. This is probably a good time to decide whether to go for a mini- or a full review. Some journals are now favouring the publication of rather short reviews focusing on the last few years, with a limit on the number of words and citations. A mini-review is not necessarily a minor review: it may well attract more attention from busy readers, although it will inevitably simplify some issues and leave out some relevant material due to space limitations. A full review will have the advantage of more freedom to cover in detail the complexities of a particular scientific development, but may then be left in the pile of the very important papers “to be read” by readers with little time to spare for major monographs.

There is probably a continuum between mini- and full reviews. The same point applies to the dichotomy of descriptive vs. integrative reviews. While descriptive reviews focus on the methodology, findings, and interpretation of each reviewed study, integrative reviews attempt to find common ideas and concepts from the reviewed material [12] . A similar distinction exists between narrative and systematic reviews: while narrative reviews are qualitative, systematic reviews attempt to test a hypothesis based on the published evidence, which is gathered using a predefined protocol to reduce bias [13] , [14] . When systematic reviews analyse quantitative results in a quantitative way, they become meta-analyses. The choice between different review types will have to be made on a case-by-case basis, depending not just on the nature of the material found and the preferences of the target journal(s), but also on the time available to write the review and the number of coauthors [15] .

Rule 5: Keep the Review Focused, but Make It of Broad Interest

Whether your plan is to write a mini- or a full review, it is good advice to keep it focused 16 , 17 . Including material just for the sake of it can easily lead to reviews that are trying to do too many things at once. The need to keep a review focused can be problematic for interdisciplinary reviews, where the aim is to bridge the gap between fields [18] . If you are writing a review on, for example, how epidemiological approaches are used in modelling the spread of ideas, you may be inclined to include material from both parent fields, epidemiology and the study of cultural diffusion. This may be necessary to some extent, but in this case a focused review would only deal in detail with those studies at the interface between epidemiology and the spread of ideas.

While focus is an important feature of a successful review, this requirement has to be balanced with the need to make the review relevant to a broad audience. This square may be circled by discussing the wider implications of the reviewed topic for other disciplines.

Rule 6: Be Critical and Consistent

Reviewing the literature is not stamp collecting. A good review does not just summarize the literature, but discusses it critically, identifies methodological problems, and points out research gaps [19] . After having read a review of the literature, a reader should have a rough idea of:

• the major achievements in the reviewed field,
• the main areas of debate, and
• the outstanding research questions.

It is challenging to achieve a successful review on all these fronts. A solution can be to involve a set of complementary coauthors: some people are excellent at mapping what has been achieved, some others are very good at identifying dark clouds on the horizon, and some have instead a knack at predicting where solutions are going to come from. If your journal club has exactly this sort of team, then you should definitely write a review of the literature! In addition to critical thinking, a literature review needs consistency, for example in the choice of passive vs. active voice and present vs. past tense.

Rule 7: Find a Logical Structure

Like a well-baked cake, a good review has a number of telling features: it is worth the reader's time, timely, systematic, well written, focused, and critical. It also needs a good structure. With reviews, the usual subdivision of research papers into introduction, methods, results, and discussion does not work or is rarely used. However, a general introduction of the context and, toward the end, a recapitulation of the main points covered and take-home messages make sense also in the case of reviews. For systematic reviews, there is a trend towards including information about how the literature was searched (database, keywords, time limits) [20] .

How can you organize the flow of the main body of the review so that the reader will be drawn into and guided through it? It is generally helpful to draw a conceptual scheme of the review, e.g., with mind-mapping techniques. Such diagrams can help recognize a logical way to order and link the various sections of a review [21] . This is the case not just at the writing stage, but also for readers if the diagram is included in the review as a figure. A careful selection of diagrams and figures relevant to the reviewed topic can be very helpful to structure the text too [22] .

Rule 8: Make Use of Feedback

Reviews of the literature are normally peer-reviewed in the same way as research papers, and rightly so [23] . As a rule, incorporating feedback from reviewers greatly helps improve a review draft. Having read the review with a fresh mind, reviewers may spot inaccuracies, inconsistencies, and ambiguities that had not been noticed by the writers due to rereading the typescript too many times. It is however advisable to reread the draft one more time before submission, as a last-minute correction of typos, leaps, and muddled sentences may enable the reviewers to focus on providing advice on the content rather than the form.

Feedback is vital to writing a good review, and should be sought from a variety of colleagues, so as to obtain a diversity of views on the draft. This may lead in some cases to conflicting views on the merits of the paper, and on how to improve it, but such a situation is better than the absence of feedback. A diversity of feedback perspectives on a literature review can help identify where the consensus view stands in the landscape of the current scientific understanding of an issue [24] .

Rule 9: Include Your Own Relevant Research, but Be Objective

In many cases, reviewers of the literature will have published studies relevant to the review they are writing. This could create a conflict of interest: how can reviewers report objectively on their own work [25] ? Some scientists may be overly enthusiastic about what they have published, and thus risk giving too much importance to their own findings in the review. However, bias could also occur in the other direction: some scientists may be unduly dismissive of their own achievements, so that they will tend to downplay their contribution (if any) to a field when reviewing it.

In general, a review of the literature should neither be a public relations brochure nor an exercise in competitive self-denial. If a reviewer is up to the job of producing a well-organized and methodical review, which flows well and provides a service to the readership, then it should be possible to be objective in reviewing one's own relevant findings. In reviews written by multiple authors, this may be achieved by assigning the review of the results of a coauthor to different coauthors.

Rule 10: Be Up-to-Date, but Do Not Forget Older Studies

Given the progressive acceleration in the publication of scientific papers, today's reviews of the literature need awareness not just of the overall direction and achievements of a field of inquiry, but also of the latest studies, so as not to become out-of-date before they have been published. Ideally, a literature review should not identify as a major research gap an issue that has just been addressed in a series of papers in press (the same applies, of course, to older, overlooked studies (“sleeping beauties” [26] )). This implies that literature reviewers would do well to keep an eye on electronic lists of papers in press, given that it can take months before these appear in scientific databases. Some reviews declare that they have scanned the literature up to a certain point in time, but given that peer review can be a rather lengthy process, a full search for newly appeared literature at the revision stage may be worthwhile. Assessing the contribution of papers that have just appeared is particularly challenging, because there is little perspective with which to gauge their significance and impact on further research and society.

Inevitably, new papers on the reviewed topic (including independently written literature reviews) will appear from all quarters after the review has been published, so that there may soon be the need for an updated review. But this is the nature of science [27] – [32] . I wish everybody good luck with writing a review of the literature.

Acknowledgments

Many thanks to M. Barbosa, K. Dehnen-Schmutz, T. Döring, D. Fontaneto, M. Garbelotto, O. Holdenrieder, M. Jeger, D. Lonsdale, A. MacLeod, P. Mills, M. Moslonka-Lefebvre, G. Stancanelli, P. Weisberg, and X. Xu for insights and discussions, and to P. Bourne, T. Matoni, and D. Smith for helpful comments on a previous draft.

Funding Statement

This work was funded by the French Foundation for Research on Biodiversity (FRB) through its Centre for Synthesis and Analysis of Biodiversity data (CESAB), as part of the NETSEED research project. The funders had no role in the preparation of the manuscript.

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What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

APA7 Style resources

APA Style Blog - for those harder to find answers

1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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Engineering: The Literature Review Process

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What is a literature review and why is it important?

Further reading ....

• 2. Precision vs Retrieval
• 3. Equip Your Tool Box
• 4. What to look for
• 5. Where to Look for it
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A literature review not only summarizes the knowledge of a particular area or field of study, it also evaluates what has been done, what still needs to be done and why all of this is important to the subject.  

• The Stand-Alone Literature Review A literature review may stand alone as an individual document in which the history of the topic is reported and then analyzed for trends, controversial issues, and what still needs to be studied.  The review could just be a few pages for narrow topics or quite extensive with long bibliographies for in-depth reviews.   In-depth review articles are valuable time-savers for professionals and researchers who need a quick introduction or analysis of a topic but they can be very time-consuming for authors to produce. Examples of review articles:   Walker, Sara Louise (2011)   Building mounted wind turbines and their suitability for the urban scale - a review of methods of estimating urban wind resource .   Energy and Buildings  43(8):1852-1862. For this review, the author focused on the different methodologies used to estimate wind speed in urban settings.  After introducing the theory, she explained the difficulty for in-situ measuring, and then followed up by describing each of the different estimation techniques that have been used instead.  Strengths and weaknesses of each method are discussed and suggestions are given on where more study is needed.   Length: 11 pages. References: 59. Calm, J.M. (2008)   The next generation of refrigerants - historical review, considerations, and outlook.   International Journal of Refrigeration  31(7):1123-1133. This review focuses on the evolution of refrigerants and divides the evolution into 4 generations.  In each generation the author describes which type of refrigerants were most popular and discusses how political, environmental, and economic issues as well as chemical properties effected choices.  Length: 11 pages.  References: 51.  
• The Literature Review as a Section Within a Document Literature reviews are also part of dissertations, theses, research reports and scholarly journal articles; these types of documents include the review in a section or chapter that discusses what has gone before, how the research being presented in this document fills a gap in the field's knowledge and why that is important.   Examples of literature reviews within a journal article:  Jobert, Arthur, et al. (2007) Local acceptance of wind energy: factors of success identified in French and German case studies.  Energy Policy  35(5):2751-2760.  In this case, the literature review is a separate, labeled section appearing between the introduction and methodology sections.  Peel, Deborah and Lloyd, Michael Gregory (2007)   Positive planning for wind-turbines in an urban context.   Local Environment  12(4):343-354. In this case the literature review is incorporated into the article's introduction rather than have its own section.   Which version you choose (separate section or within the introduction) depends on format requirements of the publisher (for journal articles), the ASU Graduate College and your academic unit (for ASU dissertations and theses) and application instructions for grants.   If no format is specified choose the method in which you can best explain your research topic, what has come before and the importance of the knowledge you are adding to the field.    Examples of literature reviews within a dissertation or thesis :  Porter, Wayne Eliot (2011)   Renewable Energy in Rural Southeastern Arizona: Decision Factors: A Comparison of the Consumer Profiles of Homeowners Who Purchased Renewable Energy Systems With Those Who Performed Other Home Upgrades or Remodeling Projects .    Arizona State University, M.S. Thesis.  This author effectively uses a separate chapter for the literature review for his detailed analysis.  Magerman, Beth (2014)   Short-Term Wind Power Forecasts using Doppler Lidar.   Arizona State University, M.S. Thesis. The author puts the literature review within Chapter Two presenting it as part of the background information of her topic.   Note that the literature review within a thesis or dissertation more closely resembles the scope and depth of a stand- alone literature review as opposed to the briefer reviews appearing within journal articles.  Within a thesis or dissertation, the review not only presents the status of research in the specific area it also establishes the author's expertise and justifies his/her own research.   

Online tutorials:

• Literature Reviews: An Overview for Graduate Students Created by the North Caroline State University Libraries

Other ASU Library Guides: 

• Literature Reviews and Annotated Bibliographies More general information about the format and content of literature reviews; created by Ed Oetting, History and Political Science Librarian, Hayden Library. ​

Readings: 

• The Literature Review: A Few Tips on Conducting It Written by Dena Taylor, Health Sciences Writing Centre, University of Toronto
• Literature Reviews Created by The Writing Center at the University of North Carolina, Chapel Hill. 
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Literature Review: Conducting & Writing

• Sample Literature Reviews
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• Finding "The Literature"
• Organizing/Writing
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Sample Lit Reviews from Communication Arts

Have an exemplary literature review.

• Literature Review Sample 1
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Have you written a stellar literature review you care to share for teaching purposes?

Are you an instructor who has received an exemplary literature review and have permission from the student to post?

Please contact Britt McGowan at [email protected] for inclusion in this guide. All disciplines welcome and encouraged.

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Complicated Treatment Course of Severe Asymptomatic Hypertriglyceridemia: A Case Report and Literature Review

Affiliations.

• 1 Department of Internal Medicine, Saint Michael's Medical Center, Newark, NJ, USA.
• 2 Department of Internal Medicine, Division of Gastroenterology and Hepatology, Saint Michael's Medical Center, Newark, NJ, USA.
• 3 Department of Medicine, Medical College Jordan University of Science and Technology, Irbid, Jordan.
• 4 Department of Medicine, Medical College Mutah University, Karak, Jordan.
• PMID: 38620025
• PMCID: PMC11034391
• DOI: 10.12659/AJCR.943858

BACKGROUND Close observation, statins, fibrate treatment, and lifestyle changes can safely manage asymptomatic individuals with severe hypertriglyceridemia (HTG) and minimal risk of symptom development. However, the risk of medication-induced liver injury in patients taking statin-fibrate makes management more challenging, and may require hospital admission and close monitoring with follow-up. CASE REPORT We present a rare case of a 43-year-old man with asymptomatic severe HTG exceeding 11.370 mg/dL with mixed hyperlipidemia, managed initially with high-intensity statins and fibrate. However, due to the concurrent use of statin and fibrates, the patient subsequently developed an acute liver injury. Hence, the oral medications had to be stopped, and the patient was admitted to the hospital for an insulin drip. Even during the hospital course, the patient's triglyceride (TG) levels showed resistance to the recommended dose of insulin and he required a higher insulin dose. He was discharged on fenofibrate and subcutaneous insulin to keep the TG level under 500. Fibrate was stopped, and high-intensity statin was used as primary prevention with lifestyle modifications. CONCLUSIONS This instance highlights the necessity of increased cognizance and cooperative endeavors in handling severe asymptomatic HTG. Our results highlight the significance of further research into the management of severe asymptomatic HTG in cases of injury to the liver. This work adds essential knowledge to the ongoing discussion about managing a rare case complicated by acute liver injury.

Publication types

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• Fenofibrate* / therapeutic use
• Hydroxymethylglutaryl-CoA Reductase Inhibitors* / therapeutic use
• Hyperlipidemias* / complications
• Hypertriglyceridemia* / complications
• Hypertriglyceridemia* / drug therapy
• Insulins* / therapeutic use
• Hydroxymethylglutaryl-CoA Reductase Inhibitors
• Fenofibrate

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Article Contents

Introduction, case report, conflict of interest statement, cecal volvulus as a rare complication of internal hernia after roux-en-y gastric bypass: a case report and literature review.

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Marvin Heck, Benjamin C Kensing, Hishaam N Ismael, Cecal volvulus as a rare complication of internal hernia after Roux-en-Y gastric bypass: a case report and literature review, Journal of Surgical Case Reports , Volume 2024, Issue 4, April 2024, rjae252, https://doi.org/10.1093/jscr/rjae252

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This case report describes a rare instance of cecal volvulus resulting from an internal hernia through Petersen’s space, occurring 20 years after Roux-en-Y gastric bypass surgery, marking it as the second such case in English literature. An 81-year-old female presented with symptoms of bowel obstruction, and imaging findings concerning for cecal volvulus. Emergency surgery revealed necrotic bowel due to an internal hernia, necessitating a right hemicolectomy, with subsequent successful anastomosis and hernia defect closure. The incidence of internal hernias post-gastric bypass is notable, emphasizing the critical need for surgical vigilance. This case underscores the importance of considering internal hernias in differential diagnoses for bowel obstruction in post-bariatric surgery patients, highlighting the life-saving role of prompt surgical intervention in the management of cecal volvulus complications.

Cecal volvulus is a rare but potentially life-threatening condition characterized by torsion of the cecum around its mesentery, leading to bowel obstruction and ischemia. While cecal volvulus itself is an uncommon clinical entity, its occurrence as a complication of an internal hernia is even more unusual. This report presents the unique case of a cecal volvulus from an internal hernia of the terminal ileum, cecum and ascending colon via Petersons space after Roux-en-Y gastric bypass surgery 20 years prior, a commonly performed surgery for morbid obesity. To our knowledge, this is only the second case reported in the English literature [ 1 ].

The patient is an 81-year-old female with a medical history significant for dilated cardiomyopathy, HFrEF, HTN, HLD, severe prosthetic aortic valve stenosis, who presented to the ED with diffuse abdominal pain, obstipation, and multiple episodes of emesis for ~24 h. Her surgical history included a Roux-en-Y gastric bypass 20 years ago (2003) complicated by small bowel obstruction requiring exploratory laparotomy in 2018.

Upon evaluation in the ED, she was a frail, ill appearing Caucasian female. Afebrile and hemodynamically stable with abdominal distension, diffuse tenderness, and voluntary guarding. On labs, the patient had a normal white count and lactate.

Computed tomography (CT) of her abdomen and pelvis with contrast revealed a dilated colon in the left upper quadrant with mesenteric edema and free fluid throughout the abdomen consistent with a cecal volvulus ( Fig. 1 ).

Computed tomography showing cecal volvulus secondary to internal hernia.

The patient was taken for emergent exploration. Upon entry to the abdomen, a large amount of purulent drainage was encountered. The cecum and terminal ileum were in the left upper quadrant, and it became clear that this was an internal hernia through Petersen’s defect ( Fig. 2 ). The right colon and terminal ileum were necrotic, the hernia was reduced, a right hemicolectomy was performed, the patient was left in discontinuity, and a temporary closure device was placed to perform a second look 24 hours after the index surgery. At her second surgery, a stapled ileocolic anastomosis was created, the Petersen’s defect was closed with an absorbable running suture, and the abdomen was closed. The patient recovered without complication and was discharged home on postoperative day 5.

Cecal volvulus through Petersen’s defect.

Internal hernias following Roux-en-Y gastric bypass surgery represent a significant and potentially life-threatening complication. The cumulative incidence of internal hernia at 3 years post-laparoscopic roux-en-y gastric bypass has been shown to be around 5% in a recent retrospective analysis of a large database that included 46 918 patients [ 2 ]. This is similar to the reported incidence of 6.2% in other single institution and single surgeon case series [ 3 ].

The literature suggests that certain surgical techniques can influence the risk of developing an internal hernia. Antecolic Roux limb placement is generally associated with a lower incidence of internal hernia compared with the retrocolic approach [ 4 , 5 ]. A recent large meta-analysis compared the incidence of internal hernias after Roux-en-Y gastric bypass surgery after mesenteric defect closure vs no closure and found a reduced incidence of 2% in patients who underwent defect closure vs 6% in non-closure [ 6 ]. A Swedish randomized controlled trial evaluated the incidence of major postoperative complications and small bowel obstruction within 3 years. The study showed that closure of the mesenteric defects leads to increased risk of early postoperative complications, mainly due to kinking of the jejunojejunostomy, but overall, significantly reduced the need for reoperation for small bowel obstruction over 3 years [ 4 ]. Despite this, no surgical technique has been proven to eliminate the risk of developing an internal hernia entirely. Patients most commonly present with internal hernias within the first 3 years after bariatric surgery secondary to intra-abdominal fat loss [ 2 ], especially if excess weight loss occurs rapidly, defined as greater than 90th percentile of expected weight loss [ 7 ].

Cecal volvulus in contrast to sigmoid volvulus is a surgical emergency due to low effectiveness of endoscopic detorsion and high risk of perforation, which can be attempted first in uncomplicated sigmoid volvulus. Colonoscopy does also evaluate the viability of the sigmoid colon. In the absence of colonic necrosis, detorsion can be attempted and semi-elective sigmoidectomy can be performed [ 8 ].

In this case, the patient presented with gangrenous bowel and required a right hemicolectomy. The patient was closed temporarily and underwent a second procedure due to the excessive amount of contamination encountered during the index operation. Detorsion and cecopexy without resection have been described for cecal volvulus but have a high risk of recurrence and are therefore not recommended [ 9 ].

None declared.

Rehfuss JP , Friedman JE , Tan SA , et al.  Cecal volvulus caused by internal herniation after roux-en-y gastric bypass surgery . J Surg Case Rep 2018 ; 2018 . https://doi.org/10.1093/jscr/rjy241 .

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Ende V , Devas N , Zhang X , et al.  Internal hernia trends following gastric bypass surgery . Surg Endosc 2023 ; 37 : 7183 – 91 . https://doi.org/10.1007/s00464-023-10206-7 .

Bauman RW , Pirrello JR . Internal hernia at Petersen's space after laparoscopic roux-en-Y gastric bypass: 6.2% incidence without closure—a single surgeon series of 1047 cases . Surg Obes Relat Dis 2009 ; 5 : 565 – 70 . https://doi.org/10.1016/j.soard.2008.10.013 .

Stenberg E , Szabo E , Ågren G , et al.  Closure of mesenteric defects in laparoscopic gastric bypass: a multicentre, randomised, parallel, open-label trial . Lancet 2016 ; 387 : 1397 – 404 . https://doi.org/10.1016/S0140-6736(15)01126-5 .

Geubbels N , Lijftogt N , Fiocco M , et al.  Meta-analysis of internal herniation after gastric bypass surgery . Br J Surg 2015 ; 102 : 451 – 60 . https://doi.org/10.1002/bjs.9738 .

Muir D , Choi B , Clements C , et al.  Mesenteric defect closure and the rate of internal hernia in laparoscopic roux-en-Y gastric bypass: a systematic review and meta-analysis . Obes Surg 2023 ; 33 : 2229 – 36 . https://doi.org/10.1007/s11695-023-06597-0 .

Schneider C , Cobb W , Scott J , et al.  Rapid excess weight loss following laparoscopic gastric bypass leads to increased risk of internal hernia . Surg Endosc 2011 ; 25 : 1594 – 8 . https://doi.org/10.1007/s00464-010-1444-9 .

Underhill J , Munding E , Hayden D . Acute colonic pseudo-obstruction and volvulus: pathophysiology, evaluation, and treatment . Clin Colon Rectal Surg 2021 ; 34 : 242 – 50 . https://doi.org/10.1055/s-0041-1727195 .

Perrot L , Fohlen A , Alves A , Lubrano J . Management of the colonic volvulus in 2016 . J Visc Surg 2016 ; 153 : 183 – 92 . https://doi.org/10.1016/j.jviscsurg.2016.03.006 .

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• Case Report
• Open access
• Published: 22 April 2024

Post-COVID reactivation of latent Bartonella henselae infection: a case report and literature review

• Yanzhao Dong 1 ,
• Ahmad Alhaskawi 1 ,
• Xiaodi Zou 2 ,
• Haiying Zhou 3 ,
• Sohaib Hasan Abdullah Ezzi 4 ,
• Vishnu Goutham Kota 5 ,
• Mohamed Hasan Abdulla Hasan Abdulla 5 ,
• Alenikova Olga 6 ,
• Sahar Ahmed Abdalbary 7 &

BMC Infectious Diseases volume  24 , Article number:  422 ( 2024 ) Cite this article

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Cat scratch disease (CSD) is caused by Bartonella henselae ( B. henselae ) and presents as lymphadenopathy following close contact with cats. However, in context of the global COVID-19 pandemic, clinical manifestations of CSD may vary, posing new challenges for healthcare professionals. Here we describe a case of a 54-year-old male with painful left upper arm mass, which gradually resolved until he was infected with COVID-19. The mass then rapidly progressed before admission. Meanwhile, pulmonary symptoms including pleural effusion emerged simultaneously. The cause was undetermined with routine blood culture and pathological test until the next generation sequencing (NGS) confirmed the presence of B. henselae . We believe this case is the first to report localized aggravation of CSD after COVID-19 infection and hopefully, offers treatment experience for clinicians worldwide.

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Introduction

Cat-scratch disease (CSD), an uncommon infection often observed in households with domestic cats, is first described in 1950 by Debré R. et al. [ 1 ]. The causative pathogen of CSD is Bartonella henselae ( B. henselae ), a Gram-negative rod that can be detected by immunohistochemistry and several silver staining methods including Warthin-Starry stain, Steiner stain and Dieterle stain [ 2 ]. At the early stage of infection, CSD normally presents as non-specific lymphadenopathy affecting both adults and children [ 3 ]. As an infectious disease, CSD has been reported worldwide and higher incidents are reported in the autumn and winter, perceivably associated the seasonal breeding of domestic cats [ 4 ].

CSD is commonly seen among young adults and children, and the major clinical manifestations of CSD include a papule at the site of microbe entrance and axillary node lymphadenopathy, which could progress to fever, aches, nausea, abdominal pain and malaise [ 5 ]. Diagnosis of CSD is usually dependent on both history of cat contact and primary lesions followed by regional lymphadenopathy, which can be further confirmed via serological evidence, blood or suppuration culture, and the next generation sequencing (NGS). However, B. henselae is a slow-growing bacterium, and bacterial culture could take up to 21 days, with a high false-negative rate. While serological tests could aid in the diagnosis, they often fail to differentiate between B. henselae and other Bartonella species. Furthermore, positive serological results may persist for years after treatment. In contrast, NGS is a highly accurate method for identifying various pathogens including B. henselae . Additionally, NGS can provide quantitative data regarding the detected pathogen, serving as an indicator of the infection’s severity. This quantitative information can be invaluable in monitoring the status of the infection. Approximately 90% of untreated lymphadenitis and lymph node enlargement following CSD gradually regress to normal size in immunocompetent patients over a period of several months, while the remaining 10% patients could progress to cutaneous erythema and result in spontaneous suppuration [ 6 ]. In these cases, the combined use of azithromycin and rifampin orally or intravenously is recommended, although the dosage and course may vary [ 7 , 8 ].

While CSD is the most common manifestation of bartonellosis and over 90% cases of CSD are benign and self-limiting, the spectrum of bartonellosis is expanding as several studies and cases have elucidated association between Bartonella infection and cardiovascular, neurological, psychiatric, ocular and rheumatic disorders [ 9 , 10 , 11 , 12 , 13 ]. For immunocompromised patients, B. henselae infection elicits vasoproliferative responses instead of localized lymphadenopathy, and manifests as a cutaneous angiogenic lesion with inflammatory cell infiltrates [ 1 ]. What is causing this phenomenon, however, is still under debate. Moreover, disseminated bartonellosis has been observed in several cases of patients with human immunodeficiency virus (HIV) infection, and one of the cases reported rapid exacerbation to respiratory failure and ultimately, death of the patient [ 14 , 15 , 16 ]. As our understanding grows, it is being increasing acknowledged that bartonellosis is a major public health issue, and efforts made to better comprehend its reservoir and vector can be assimilated into solving this problem [ 17 ].

Since its discovery, CSD has been studied comprehensively by research groups across the world. Nevertheless, little is known about CSD progression in the context of Coronavirus disease 2019 (COVID) infection, with only one case report available on coinfection of COVID and B. henselae in 2021 [ 18 ]. We believe that this is the first case to report reactivation of B. henselae post COVID infection.

Case presentation

On January 31, 2023, a previously healthy male was admitted with a one-month history of red and swollen mass on the ulnar side of left upper arm. At the onset of the swollen mass, he visited the local clinic and ultrasound (US) examination was ordered, indicating inflammation with abscess formation. Therefore, he was prescribed with oral administration of cefuroxime (250 mg, BID) for 7 days and pain relief treatment (irecoxib, 100 mg, BID). The mass gradually resolved until shortly progression complicated with symptoms of fever (Tmax = 39.5 °C), cough, fatigue, myalgia, shortness of breath and anorexia, which was confirmed to be COVID infection by local hospital. During this period, he observed rapid progression of the original mass with both an increase in size and the formation of a purulent spot. In search of second medical opinion, he visited our out-patient clinic. Prehospital magnetic resonance imaging (MRI) indicated soft tissue swelling on the ulnar side of the left upper arm, with an internal mass-like elongated T2 signal and cellulitis-like enhancement on the enhancement imaging. He recalled no history of distant travel, animal bites or scratches. As a construction worker, he was generally well and the only significant medical history was lumbar disc herniation microdiscectomy he received 10 years ago.

On admission, the patient complained of coughing with white sputum, severe anorexia and nausea. Worse even, the mass had ruptured on the way to hospital, and he had to covered it with some gauze. During the dressing change, it was observed that the mass was swollen with a sinus tract, and approximately 15 mL exudate was drained. The exudate was initially purulent and became hemopurulent on pressure. Physical examination revealed lymphadenopathy in the unilateral axillary and supratrochlear lymph nodes, with local redness and tenderness around the abscess. Subcutaneous edema on the ulnar side of the left upper arm and forearm was observed. Lung auscultation showed scattered rales in both lungs, occasionally with wheezing. Pre-operative blood tests showed elevated white blood cell count (WBC) of 13.08*10 9 /L (normal range 4.0–10.0*10 9 /L), elevated C reactive protein (CRP) of 37.54 mg/L (normal range 0.00–8.00 mg/L) and negative result of HIV infection. Meanwhile, the patient showed no signs of fever (Temperature = 36.6 °C). Pulmonary CT scan showed inflammation on both lungs with interlobular and pleural effusion. Therefore, the patient was started empirically on intravenous infusion of piperacillin/tazobactam for the lesion and possible lower respiratory tract infection. On day 2 of admission, the first surgery was performed, where an extended incision was made to expose the subcutaneous fascia, revealing large amount of inflamed granulation tissue. The ulnar nerve was intact but adherent to surround tissue, and careful dissection was performed to free the ulnar nerve and avoid nerve damage. After excision of necrotic tissue, the abscess cavity was repeatedly irrigated and covered with vacuum sealing drainage (VSD) device. The excised tissue was then set for NGS, pathological tests and bacterial culture (Fig.  1 ).

( A) : MRI image of the mass on admission; ( B ): Preoperative view of the mass, the pus head has ruptured; ( C) : Intra-operative view of the mass, most necrotic or infected tissue have been removed; ( D) : Post-operative histopathological results showing acute and chronic inflammation of subcutaneous soft tissue with histiocytes infiltration (marked by green triangle and magnification on the upper right corner), regional inflammatory granulation tissue hyperplasia (marked by red star)

In the meantime, on day 4 of hospitalization, the patient complained of shortness of breath with decreased blood oxygen saturation levels, and an urgent pulmonary CT scan was ordered. The repeated CT report showed progressed bilateral pleural and interlobar effusions with atelectasis of both lower lobes, and a new ground-glass opacity in the apical segment of the right upper lobe, suggestive of inflammatory changes. At consultation in respiratory medicine experts, bilateral thoracentesis and placement of chest drainage tubes was ordered, and a total of 1100 mL yellow clear pleural effusion was drained on the first day. The pleural drainage was collected and underwent routine, biological examination and bacterium culture, indicating Non-septic Exudative Pleural Effusion. Multiple tissue sample were sent for testing and culture, and the NGS result on day 5 reported presence of B. henselae in the abscess, which confirmed the diagnosis of CSD. Further inquiry on medical history revealed that the patient owned a rural warehouse where he kept clothing and bed sheets, and a pet cat, although he remembered frequent visit of local feral cats. The warehouse was relatively poor in terms of air flow, where he would take occasional naps. After alteration of antibiotic plan to doxycycline combined with azithromycin, the pulmonary distress gradually resolved and inflammatory indicators reduced to normal level on day 8 (CRP: 0.49 mg/L; WBC 5.02*10 9 /L).

On day 8 of admission, the patient reported relief from chest tightness and shortness of breath, and a repeated CT showed interstitial changes in both lungs without pleural effusion on day 8 of admission (Fig.  2 ). The bilateral chest drainage tubes were then removed.

Pulmonary CT scan results with effusion indicated by red arrows. A : Taken 2 days prior to admission, showing interstitial changes, pneumonia with minor amount of pleural effusion; ( B) : Taken on day 4 of admission, showing progressed pneumonia with increased pleural effusion; ( C) : Taken on day 8 of admission, showing alleviated pneumonia, and previous pleural effusion absorbed; ( D) : Taken 2 weeks after discharge with normal result

Meanwhile, as the pulmonary symptoms relieved, the patient underwent secondary debridement, which showed localized inflammation and limited residual granulation tissue, and the remaining necrotized tissue was removed before suturing. The patient was generally well after the second surgery and discharged on day 11 of admission.

On out-patient follow-up 2 weeks later, the patient recovered from the previous symptoms. Physical examination showed negative pulmonary signs, and the incision healed without further inflammation.

CSD has been reported to cause pleural effusion possibly due to obstructed lymphatic drainage from the lungs [ 19 ]. In this case, the pulmonary CT scan on day 4 of admission showed interstitial inflammation with bilateral pulmonary effusion, indicating a possible role of COVID infection. This phenomenon was also observed in canine, as reported by Cherry N. et al. in 2009 [ 20 ]. Interestingly, a canine study led by Weeden A. et al. indicated positive B. henselae DNA in pleural and peritoneal effusion while pericardial effusion showed negative results [ 21 ]. In our case, the recurrence of localized mass and subsequent pleural effusion was parallel to COVID infection, possibly due to disrupted immune response.

As a zoonotic pathogen, B. henselae is transmitted to cats by flea feces contamination and ingested while grooming, therefore transmission to human is often achieved by cat scratches and bites [ 22 , 23 ]. This was corroborated by Chomel B. et al. in 1996, where they observed transmission of B. henselae to specific-pathogen-free (SPF) cats through contact with infected flea. They also noted that highly bacteremic cats, in absence of fleas, were unable to infect SPF cats [ 24 ]. The seasonality of CSD diagnosis, interestingly, has also been extensively studied by Nelson A., Saha S. and Mead P. in the United States spanning from 2005 to 2013 [ 25 ]. It was observed that the largest proportion of CSD diagnosis was made during January, followed by August and November, which they attributed to adoption pattern and age susceptibility of kittens, and peaking of fleas during fall and winter [ 26 ]. This is in line with our patient, who was also admitted in January.

In terms of source of infection, our patient denied cat scratch or bite on admission, whereas indirect contact with cats was found possible in his warehouse. The indirect mode of B. henselae transmission in this case was recently reported by Bush J. et al. in 2023, and they revealed the ability of B. henselae to exist stably in several biological and non-biological fluids [ 27 ]. While the discovery is exhilarating, the possibility of indirect B. henselae transmission poses a challenge for clinicians in face of similar patients without relevant history of feline contact.

Infection of B. henselae could cause diverse clinical symptoms depending on the age group, where children and younger individuals are prone to develop lymphadenitis while the elderly are more likely to suffer from endocarditis, and combined with B. quintana account for over 90% Bartonella endocarditis cases [ 28 ]. While it is necessary to consider infection of Bartonella species in the differential diagnosis in patients with fever of unknown causes, CSD is often misdiagnosed since the diagnosis is critically dependent on serological tests or polymerase chain reaction (PCR) assay as routine blood culture methods fails to detect B. henselae [ 5 ]. While serological test often shows high sensitivity, it fails to distinguish from ongoing infection and past infection. On the other hand, PCR assay has been shown to detect B. henselae in fresh tissue or purulent sample with high sensitivity and specificity, as reported by Gaoz S. et al. in 2022 [ 29 ]. The major challenge for clinicians and microbiologists is that PCR requires specific target, which is sometimes unidentified initially. Another factor for PCR sensitivity is the type of sample, since Khalfe N. and Lin D. observed decreased PCR sensitivity in paraffin embedded sample fixed by formalin [ 30 ]. In comparison, NGS could detect the species of pathogen with a quantity profile, offering assistance for clinicians to narrow down suspected pathogens at an early stage of diseases.

COVID has been characterized as a highly transmissible emerging pathogen, causing mild to severe respiratory symptoms with or without systematic complications and spreading fast across the world [ 31 ]. In context of the global pandemic of COVID, the incidence of various disease has surged due to a variety of reasons. A national study in Argentina in 2022 reported that COVID pandemic is associated with increased incidence of CSD, which was attributed to the prolonged cat contact due to quarantine, and higher rates of systematic CSD, which is yet to be explained [ 32 ].

In conclusion, we present a case underscoring the importance of vigilance in diagnosing and managing unusual presentations of less common diseases, especially in the context of the COVID-19 pandemic. While CSD is typically a self-limiting condition, this case was complicated by COVID-19, leading to unique challenges in both diagnosis and treatment. The co-occurrence of these two conditions highlights the complexity of managing infectious diseases in a time of a global pandemic. Clinicians, hence, should consider multiple diagnostic possibilities and adapt treatment strategies accordingly.

Availability of data and materials

The dataset supporting the conclusions of this article is included with the article.

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Department of Orthopedics, The First Affiliated Hospital, Zhejiang University, #79 Qingchun Road, Hangzhou, Zhejiang Province, 310003, People’s Republic of China

Yanzhao Dong, Ahmad Alhaskawi & Hui Lu

The Second Affiliated Hospital of Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, 310003, People’s Republic of China

School of Biomedical Science, Faculty of Medicine, The Chinese University of Hong Kong, Rm 706, 7/F, Lo Kwee-Seong Integrated Biomedical Science Bldg, Shatin, New Territories, Hong Kong, China

Haiying Zhou

Department of Orthopedics, Third Xiangya Hospital, Central South University, #138 Tongzi po Road, Changsha, Hunan Province, 410013, People’s Republic of China

Sohaib Hasan Abdullah Ezzi

Zhejiang University School of Medicine, #866 Yuhangtang Road, Hangzhou, Zhejiang Province, 3100058, People’s Republic of China

Vishnu Goutham Kota & Mohamed Hasan Abdulla Hasan Abdulla

Department of Neurology, Republican Research and Clinical Center of Neurology and Neurosurgery, Skoriny, Minsk, Belarus

Alenikova Olga

Department of Orthopedic Physical Therapy, Faculty of Physical Therapy, Nahda University in Beni Suef, Beni Suef, Egypt

Sahar Ahmed Abdalbary

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Hui Lu designed the study; Yanzhao Dong and Ahmad Alhaskawi drafted the manuscript, Xiaodi Zou and Haiying Zhou performed literature selection and drew the figures; Sohaib Hasan Abdullah Ezzi and Vishnu Goutham Kota collected patient data, Sahar Ahmed Abdalbary, Alenikova Olga and Mohamed Hasan Abdulla Hasan Abdulla revised the manuscript. The authors have read and approved the final manuscript.

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Dong, Y., Alhaskawi, A., Zou, X. et al. Post-COVID reactivation of latent Bartonella henselae infection: a case report and literature review. BMC Infect Dis 24 , 422 (2024). https://doi.org/10.1186/s12879-024-09336-7

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DOI : https://doi.org/10.1186/s12879-024-09336-7

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• Cat scratch disease (CSD)
• Bartonella henselae
• High-throughput sequencing

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Microblading reaction as a manifestation of systemic sarcoidosis: two case reports and a review of the literature

• Eva Klara Merzel Šabović   ORCID: orcid.org/0000-0002-1634-1868 1 , 2 ,
• Mateja Starbek Zorko 1 , 2 ,
• Violeta Hosta 1 ,
• Borut Žgavec 1 &
• Vid Bajuk 1 , 2  

Journal of Medical Case Reports volume  18 , Article number:  221 ( 2024 ) Cite this article

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Sarcoidosis is a multisystemic disease characterized by granulomatous inflammation. Sarcoidosis often poses a diagnostic challenge owing to its nonspecific or mild clinical features. In 20–35% of cases, sarcoidosis initially presents on skin. However, skin lesions commonly mimic dermatological conditions. Therefore, it is important to not underestimate the skin manifestations and perform histopathological examinations to make a timely diagnosis.

Case presentation

We present two cases of 33-year-old Caucasian female patients with orange–red macules and plaques that developed in the eyebrow area 1 and 6 years after microblading, respectively. Histopathological examination confirmed a diagnosis of sarcoidosis. The lymph nodes and lungs were also affected in both patients.

Our two reports suggest that an esthetic procedure involving dermal or subcutaneous injection of foreign materials can trigger the development of cutaneous and systemic sarcoidosis. However, this relationship has not been described yet. Physicians should, therefore, be aware of this complication to properly evaluate and treat such patients in a timely manner.

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Introduction

Sarcoidosis is a complex disease with unknown etiology and pathogenesis. Several factors may contribute to the development of sarcoidosis, such as a genetic predisposition with certain human leukocyte antigen (HLA) genotypes [ 1 ] and/or environmental factors, such as mycobacterial or propionibacterial organisms [ 2 ]. In addition, there is evidence suggesting an autoimmune or immune-mediated genesis of the disease [ 3 ]. In sarcoidosis, both the innate and adaptive immune systems are involved, highlighting the complexity of the pathogenesis of sarcoidosis [ 4 ]. Nevertheless, the specific causes that trigger the development of the granulomatous/fibrotic process in sarcoidosis remain unknown [ 4 ]. The prevalence of sarcoidosis varies by geographic location, with Scandinavian countries having the highest prevalence of 140–160 per 100,000 persons, while the prevalence in South Korea, Taiwan, and Japan is 1–5 per 100,000 [ 5 ].

Sarcoidosis is most commonly present in a mild form. However, in some cases, it can also be lethal, primarily because of the cardiac involvement. It is characterized by noncaseating granulomatous inflammation, which most commonly affects the lungs, lymph nodes, eyes, and skin [ 6 ]. The etiology of this condition is still not entirely understood. Sarcoidosis is believed to be triggered by exposure to extrinsic antigens in immunogenetically susceptible individuals [ 7 ]. According to previous studies, extrinsic antigens are the most common microbial agents and environmental substances [ 8 ]. In the developed world, there are growing reports of esthetic procedures with dermal infiltration, which might act as an extrinsic agent triggering sarcoidosis in predisposed individuals [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Here, we present two cases of a 33-year-old female patient who presented with orange–red maculopapular lesions in the eyebrow area after microblading. To date, only one case of cutaneous sarcoidosis after microblading has been reported [ 17 ]. However, no cases of systemic sarcoidosis after microblading, as in our two cases, have been reported.

A 33-year-old Caucasian female patient presented with orange–red slightly infiltrated plaques in the eyebrow region that had been present for 3 years (Fig.  1 ). The plaques occurred 1 year after semipermanent tattooing—microblading, which had been performed only once. The skin was thoroughly examined, and the skin lesions were present only in the eyebrow area. First, allergic contact dermatitis was suspected and excluded using patch testing. Owing to the specific color of the lesions, a sarcoid granulomatous reaction was suspected. A thorough occupational and travel history was obtained, with no evidence of external influences that might cause sarcoidosis. Family history was negative for sarcoidosis. Her medical history was otherwise unremarkable. However, she reported a breast augmentation procedure that had been performed two years before the appearance of the skin lesions. A biopsy of the skin lesions revealed granulomatous dermatitis with epithelioid (sarcoid) granulomas (Fig.  2 ). Accordingly, sarcoidosis was suspected and the patient was referred for laboratory workup and chest radiography. Laboratory workup results were unremarkable with normal C-reactive protein (< 5 mg/L), normal angiotensin-converting enzyme (0.50 µkat/L), normal levels of serum calcium (2.37 mmol/L), magnesium (0.71 mmol/L), potassium (4.9 mmol/L), and sodium (137 mmol/L). However, chest radiography revealed hilar lymphadenopathy and reticulonodular opacities in the lungs, consistent with grade II sarcoidosis. She denied any pulmonary symptoms. Additionally, the patient was examined for other manifestations of sarcoidosis, which were excluded by other specialists. She was referred to a pulmonologist who performed an additional examination that revealed the progressive nature of pulmonary sarcoidosis with initial fibrosis. The patient required systemic treatment with prednisolone at an initial dose of 16 mg daily. After three months of systemic treatment with prednisolone 16 mg daily and topical treatment with momethasone 1 mg/g cream twice weekly, resolution of the cutaneous lesions was observed (Fig.  3 ). During the 2-year follow-up period in which she received continuous systemic prednisolone, we observed no recurrence of the skin lesions despite the gradual reduction of the prednisolone dose to 6 mg every other day. In addition, the reticular pulmonary changes regressed.

The first case of a female patient with mildly infiltrated erythematous plaques in the eyebrow area with a typical orange hue

Histopathological examination of the first patient showing granulomatous dermatitis with epithelioid (sarcoid) granulomas

Resolution of cutaneous lesions in the first patient after 3 months of treatment with systemic corticosteroids

A 33-year-old Caucasian female patient presented with orange–red mildly infiltrated plaques in the eyebrow area that lasted for three months (Fig.  4 ). Upon thorough examination no other skin lesions were observed. She underwent microblading for 6 consecutive years, after which skin lesions developed. As in the first case, thorough occupational and travel histories were taken, and were unremarkable for external agents that could trigger sarcoidosis. Family history was also negative for sarcoidosis. Owing to the red–orange color of the lesions, a sarcoid granulomatous reaction was suspected and confirmed upon histopathological examination (Fig.  5 ). Laboratory workup revealed elevated erythrocyte sedimentation (34 mm/h), elevated C-reactive protein (13 mg/L), elevated angiotensin-converting enzyme (1.46 µkat/L), elevated chitotriosidase (480 nmol/h ml), and hypercalciuria (4.7 mmol/L) with a urine calcium/creatinine ratio of 0,96. Normal levels of serum calcium (2.23 mmol/L), magnesium (0.71 mmol/L), potassium (4.4 mmol/L), and sodium (139 mmol/L) were observed, however level of phosphate (0.50 mmol/L) was decreased. Furthermore, chest radiography revealed hilar lymphadenopathy and reticulonodular opacities in the lungs, which was consistent with sarcoidosis. The patient was referred to a pulmonologist who performed additional examinations and confirmed grade II sarcoidosis. However, owing to its non-progressive nature without fibrosis, treatment was not initiated at the time. Additional workup was performed for other manifestations of sarcoidosis; however, in addition to the skin, lungs, lymph nodes, and endocrine organs (hypercalciuria), other organs were not involved. Moreover, a high-resolution computed tomography scan performed 6 months after the initial diagnosis revealed resolution of sarcoidosis lesions in the lungs. For cutaneous involvement, she was prescribed mometasone furoate cream once daily for 10 days and then twice weekly as a maintenance treatment. However, no improvement was initially noted in the eyebrow area. After remission of pulmonary sarcoidosis and upon a 1-year follow-up visit, significant improvement of the skin was observed—only slight erythema of eyebrows persisted.

The second case of a female patient with mildly infiltrated erythematous plaques in the eyebrow area with a typical orange hue

Histopathological examination of the second patient showing granulomatous dermatitis with epithelioid (sarcoid) granuloma

Sarcoidosis is a disease that remains largely unknown. The most frequent question bothering both physicians and patients is its trigger. This question is particularly important because sarcoidosis is not very rare [ 5 ]. Sarcoidosis is more common in women, and its onset is often in the third or fourth decade of life [ 7 ].

Diagnosis is often delayed owing to nonspecific or mild clinical features. Sarcoidosis affects multiple organs. The most frequently involved organs were the lungs (90% of patients), lymph nodes, and eyes (60%). Sarcoidosis can also affect other organs, such as the liver and spleen, heart (20–27%), endocrine and exocrine organs (hypercalciuria and hypercalcemia in 10% of patients), nervous system (10%), bones (1–13%), upper respiratory tract (2%), and kidneys owing to renal calculi formation [ 18 ]. Skin involvement is present in 20–35% of patients [ 7 ].

Dermatologists are in a unique position to make a timely diagnosis since skin manifestations are often a presenting feature. Sarcoidosis can present with specific or nonspecific skin lesions. Specific lesions show granulomatous inflammation on biopsy, whereas nonspecific lesions manifest only as inflammatory reactions without granuloma formation [ 6 ]. The most common skin manifestations include maculopapular, plaque-like, and subcutaneous lesions and erythema. It may also present as lupus pernio or with rarer, nonspecific forms, such as psoriasiform, annular, lichenoid, verrucous, photodistributed, and ichthyosiform [ 7 ].

Sarcoidosis is thought to develop in immunogenetically susceptible individuals after exposure to extrinsic antigens. Extrinsic antigens are the most common microbial or environmental triggers [ 7 ]. Mycobacterium and Propionibacterium are the most common microbial triggers [ 8 ]. Among the environmental triggers, people who worked in areas with mold or were exposed to insecticides were more likely to develop sarcoidosis [ 19 ]. Both patients denied having lived or worked in places with mold and had unremarkable travel histories. The first patient worked as a cashier, and the second as a nurse.

In modern times, people, especially in developed countries, are less likely to be exposed to potential contaminants at work or at home but are more likely to undergo esthetic procedures. According to increasing reports in literature, esthetic procedures could serve as an extrinsic trigger for the clinical manifestation of sarcoidosis in immunogenetically susceptible individuals, as suspected in our two cases. Granulomatous reactions have been observed after tattooing [ 10 , 14 , 15 , 16 ], microneedling [ 11 , 12 , 13 ], injection of botulinum toxin [ 20 , 21 ], and injection of dermal fillers [ 9 , 22 ]. Interestingly, there is also a case report of cutaneous and pulmonary sarcoidosis after breast augmentation [ 23 ].

Microblading is a popular esthetic procedure used primarily for eyebrow restoration; however, it has also gained popularity for some dermatologic conditions, including alopecia totalis and madarosis owing to hypothyroidism or chemotherapy. Microblading is a superficial micropigmentation procedure in which pigments are introduced deep into the papillary dermis. The results are semipermanent and last 12–18 months [ 24 ]. Granulomas rarely develop at microblading sites [ 24 ]. In a recent review article, 21 cases of sarcoidosis were noted after permanent tattooing but only 1 after microblading. In the case of sarcoidosis that developed after microblading, only the skin was affected [ 17 ]. Interestingly, both patients were found to have systemic sarcoidosis. Therefore, microblading probably triggered the development of sarcoidosis in both patients. As the pigment deposit in microblading is shallower and presumably not dispersible compared to classic tattooing, resolution of granulomatous inflammation is probably more likely than in sarcoidosis after classical tattooing [ 17 , 24 ].

Common to all esthetic procedures associated with sarcoidosis appears to be infiltration of the dermis or subcutis with foreign substances that may serve as triggers for sarcoidosis. However, sarcoidosis is not always the cause of granulomatous reactions. Therefore, we propose the following clinical recommendation: when a patient presents with chronic lesions at the site of injection of foreign material, especially with skin lesions of orange–red color, the patient should be appropriately evaluated for sarcoidosis. Such an examination should initially include a biopsy, which should then guide us further toward sarcoidosis or another diagnosis. If the histopathologic examination reveals a granulomatous inflammatory infiltrate, we should exclude other diseases consisting of granulomatous inflammation, such as foreign body granulomas, infectious granulomas, and interstitial granulomatous dermatitis [ 7 , 25 ].

Treatment of patients with granulomatous reactions after dermal procedures consists of topical or oral corticosteroid therapy, or treatment with other oral immunosuppressants [ 14 ]. In patients with mild cutaneous sarcoidosis, topical or intralesional corticosteroids are used as the first-line therapy. In rapidly progressive extensive sarcoidosis or in cases of ineffective topical therapy, patients are treated with oral corticosteroids. Tumor necrosis factor-α (TNF-α) inhibitors are beneficial for treating recurrent skin lesions [ 26 ]. However, TNF-α inhibitors can sometimes even induce a paradoxical reaction with the development of a sarcoidosis-like reaction [ 27 ]. Other treatment options include antimalarials, methotrexate, tetracycline antibiotics, mycophenolate mofetil, and thalidomide [ 25 ]. Recently, treatment with Janus kinase inhibitors has been proposed to be effective [ 28 , 29 ]. Case studies have also shown a beneficial effect of treating skin lesions with psoralen plus ultraviolet A light phototherapy, photodynamic therapy, pulsed dye lasers, and CO 2 lasers [ 7 ].

Interestingly, our two cases differed significantly in the time interval between the triggering event (microblading procedure) and onset of cutaneous sarcoidosis. In the first patient, sarcoidosis manifested on the skin 1 year after the microblading procedure, whereas in the second patient, it occurred 6 years after the initial microblading procedure, which was followed by several repeated procedures in the following years. Our two cases raised some relevant questions and assumptions, even though they could not be fully explained and answered. For example, sarcoidosis may be triggered in susceptible individuals when a certain threshold for the accumulation of a foreign substance (ink) is reached. Implantation of other foreign substances, such as breast implants, as in our first patient, could increase susceptibility to cutaneous sarcoidosis triggered by microblading. This could explain why the first patient developed sarcoidosis after one procedure, whereas the second patient developed sarcoidosis after six microblading procedures. In addition, a progressive course of sarcoidosis with pulmonary fibrosis in the first patient could be a coincidence; however, it could be owing to the additive deleterious effects of multiple implanted foreign substances in addition to the effect of the long-term presence of the triggering substance, that is, the deposited skin pigment, in subsequent years. It is also unknown whether time-dependent pigment dispersion plays an important role. Therefore, long-term follow-up is required. It is difficult to predict whether skin changes will recur after discontinuation of systemic corticosteroid therapy in the first patient because local corticosteroids initially did not eliminate cutaneous sarcoidosis in the second patient. In this case, spontaneous remission of sarcoidosis was most likely the reason for the resolution of skin symptoms, which according to some reports, may be due to the high release of transforming growth factor β from alveolar macrophages [ 30 ]. However, this observation suggests that systemic corticosteroid treatment is required to treat cutaneous sarcoidosis. Therefore, more real-world data are required. However, the possibility of preexisting sarcoidosis and microblading as triggers of skin sarcoidosis in our two cases cannot be neglected. However, this assumption does not diminish the role of microblading in sarcoidosis development or progression.

In addition, it will be interesting to continue monitoring both patients, especially the first one treated with systemic corticosteroids because of progressive pulmonary involvement, to determine whether cutaneous lesions recur after treatment cessation. Depending on the transient effect of the microblading procedure, one might predict that the skin lesions will not recur; however, the pigment remains in the body because it is not eliminated from the tissues. It is difficult to predict whether the dispersed pigment acts as a trigger for sarcoidosis or not.

Because sarcoidosis most commonly affects women between the ages of 30 and 40 years, it is important to emphasize that physicians should educate all patients with sarcoidosis about potential skin complications after esthetic procedures involving infiltration of the dermis or subcutis. Other options, such as superficial peels or laser treatment, should be considered. However, further studies are needed to provide practical recommendations for esthetic procedures in patients with sarcoidosis. In addition, physicians and estheticians who perform esthetic procedures should be aware of the risk of sarcoidosis in patients with a predisposition. Prior to such procedures, patients should be adequately informed of this risk despite its rarity.

As our two cases also demonstrated, dermal or subcutaneous infiltration with foreign material during esthetic procedures can trigger the manifestation of sarcoidosis. When esthetic procedures become increasingly popular, patients with chronic lesions at the injection site of the foreign material, especially macular, papular, or nodular lesions of orange–red color, should be appropriately evaluated for possible sarcoidosis. Such an examination should initially include a biopsy, which should guide the physician in the direction of either sarcoidosis or another diagnosis. In addition, all patients with sarcoidosis should be educated and warned of such complications before undergoing esthetic procedures.

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EKMŠ reviewed the literature, wrote the initial manuscript, and managed the first patient. MSZ assisted in preparation of the final manuscript. VH and BŽ confirmed the diagnosis, analyzed, and provided histopathological images. VB reviewed the literature, managed the second patient, and completed the manuscript. All authors have read and approved the final manuscript.

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Merzel Šabović, E.K., Starbek Zorko, M., Hosta, V. et al. Microblading reaction as a manifestation of systemic sarcoidosis: two case reports and a review of the literature. J Med Case Reports 18 , 221 (2024). https://doi.org/10.1186/s13256-024-04439-w

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Received : 16 July 2023

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DOI : https://doi.org/10.1186/s13256-024-04439-w

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