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What is Unit testing?

Types of unit testing: manual and automated, why do you need unit testing, who performs unit testing, benefits of unit testing, unit testing life cycle, role of unit testing in qa strategy, different techniques of unit testing, unit testing vs integration testing, unit testing frameworks, how to perform unit testing, limitations of unit testing, best practices for unit testing.

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Frequently Asked Questions (FAQs)

Unit testing is a software testing method where individual components of the software are tested independently to verify each part functions correctly. It's a fundamental practice in software development, aimed at ensuring code quality and reliability by isolating each unit and validating its performance.

The primary objective is to isolate a code section and test its correctness. It helps uncover early bugs and flaws in application code that can be more challenging to identify in the later stages of the software testing life cycle (STLC).

Unit testing is a critical process in software development, where individual components of a program are tested in isolation to ensure they function correctly. This method, primarily performed by developers, focuses on the smallest units of code, like functions or methods, to identify and fix issues early, enhancing overall software quality. By using unit testing, developers can refine their code, simplify debugging, and provide clear documentation of their software's functionality. It's an essential practice for maintaining code integrity, facilitating efficient development, and ensuring reliable, bug-free software.

The process of running unit tests consists of four steps:

• Creating test cases : Writing multiple test cases of a web application’s components.
• Review and re-write : Review the written test cases and re-writing them if there are any mistakes
• Baseline : Checking whether each code line is in a manner or not
• Execution : Performing test execution using an online Selenium Grid .

Unit tests are designed to be run quickly and often — one at a time or all together. They need to be kept simple and clear so that they're easy to read and understand, even if they contain complicated logic or lots of variables. It is run before integration testing; therefore, it can save a lot of time and costs if done correctly. It can be carried out manually or with automated testing tools like Selenium .

Manual unit testing is a process where developers personally write and execute test cases. This method involves creating detailed test plans and offers flexibility and a deep understanding of the code. However, it can be time-consuming and less consistent, especially for larger projects. Manual testing is often preferred for smaller projects or in scenarios where detailed, hands-on examination of code is necessary.

Automated unit testing, in contrast, relies on software tools to execute pre-written tests. It is characterized by its efficiency, consistency, and ability to cover a wide range of test scenarios quickly. Automated tests are ideal for large-scale projects, offering rapid execution and detailed reporting capabilities. This method is particularly effective for regression testing and continuous integration processes.

Unit testing is often considered the first level of web application testing . If you have written a code, you must test it before releasing the software application to ensure it is working as expected.

Therefore, It is required for the following reasons:

• To catch bugs at the early stages : Since Unit testing is performed before integration testing, many errors are detected early in the development cycle.
• To make the debugging process easier and quicker : As you are testing the units and not the combined modules, it would be easier to detect the bugs. Therefore, making the debugging process easier and quicker.
• To isolate a unit of code and ensure that it works properly : It makes code more maintainable by allowing you to modify it without affecting other parts of your application.
• To test your application’s functionality : It tests every module unit before integrating it into an application. Thus, it ensures the code you write performs as it is required.
• To reduce the cost of fixing issues and save time : Integration testing is relatively high maintenance and complex. If Unit testing is in place, many defects are cleared before moving to integration. Hence, it saves a lot of time and cuts down the overall cost.

Unit testing can be performed by anyone who has access to the source code for the project or application. This includes developers, testers, and QA engineers, although it often involves a combination of these roles. Unit tests should be written by developers who know how a class, function, or module should work. Developers should also know how their code interacts with other systems, such as databases and external systems.

It happens in the development stage, saves developers time, and avoids testing code multiple times. It helps identify issues with the codebase and build and deploy new features confidently. Unit tests make the entire code maintenance easier by ensuring that newly added functionality doesn’t break the existing application’s codebase.

You can even develop new features rather than worrying about the existing code. Unit testing can also be used to shorten the debugging time and assist developers in identifying bugs and flaws in the application before releasing it to the general public.

Benefits that you can’t overlook.

• It makes the coding process agile and can be run repeatedly with relative ease
• Organizations can leverage Unit testing in their development process that helps them identify and fix issues in an earlier stage of the development cycle.
• When you write the test before the code, it makes you aware of the possible issues that might arise, leading to writing better code and improving its quality
• It saves a lot of time in performing regression testing .
• It makes the code more reliable, and if any future change occurs, developers will find it easy to detect bugs rather than repeatedly going through the entire codebase
• You can use tools while writing the unit tests to know the coverage matrix and improve it
• Unit tests provide system documentation, which helps developers read about the program's functionality or application of individual modules.
• A comprehensive set of unit test suites is a security shield for developers. By running tests frequently, they can ensure the recent changes to the codebase haven’t affected the existing system. Therefore, it contributes to higher code quality
• Unit tests can also act as documentation since they are examples of how to use applications under tests.
• It generates a more testable code, allowing you to use dependency injection

Unit testing is a fundamental part and usually the first stage in the software development life cycle. Here are the six phases of the Unit test life cycle:

• Review the code written : The life cycle of a unit test is to plan, implement, review and maintain. According to the unit test life cycle, you first outline the requirements of your code and then attempt to create a test case for each of them. You review the code written when you are done with your implementation and testing it.
• Make suitable changes : When the time comes to refactor and make suitable changes to your code, taking a quick look at the life cycle of each function or method will give you insight into what is going on in that piece of code. Here is an example:
• Parameters being passed in
• Code doing its job
• Code returning something
• Execute the test and compare the expected and actual results :: This phase of the Unit testing life cycle involves developing a test by creating a test object, selecting input values to execute the test, executing the test, and comparing the expected and actual results
• Fix the detected bugs in the code : It also gives developers peace of mind when adding or modifying code because they know if they break something, they will be notified immediately during testing. This way, you can fix problems before they ever reach production and cause issues for end users
• Re-execute the tests to verify them : Unit testing is a great way for developers to keep track of their changes, which can be especially important when it comes to life cycle methods that may not have a visual representation. Re-executing the tests to verify them after each change can help ensure everything is still working as expected. As you can see in this brief, It can make your life easier by giving you confidence that your changes haven't caused any regressions in existing functionality

It has numerous advantages over the other types of software testing techniques. By running unit tests, developers can get precise feedback and achieve high execution speed. Also, if you run unit tests that validate the functional behavior of an application, and the test fails, in most cases, you can ensure that the issue lies in the function

End-to-end testing and similar testing interact with the application just like a real user does. Therefore, it provides more realistic feedback. Furthermore, unit tests verify how different isolated modules or units function together. However, it can’t validate how these units integrate with other units. In this case, integration testing, end-to-end testing, and similar types of testing can verify how well these units integrate with different units.

By Louise J Gibbs

In a nutshell, the role of Unit testing in QA strategy is to provide fast and early feedback to developers. But you can’t rely entirely on unit tests as they lack some features in a few aspects. Therefore, an ideal approach is to back them with another type of testing in the area where unit tests fall short. Using a test pyramid can be a viable concept as it states that having a larger number of unit tests and fewer other types of tests is good.

The Unit testing techniques can be classified into three parts which help unit testers validate each unit of the application's code in isolation. These techniques fulfill different software requirements and ensure its proper functioning.

The different techniques are:

• Whitebox testing : It's also referred to as glass box or transparent testing. In this type of testing, the tester is aware of the application's internal functionality and can test it against the design and requirements. However, the internal structure of an application’s component or function to be tested is unknown.
• Black-box testing : In this type of unit testing, testers validate the software application's user interface, along with its input and output.
• Gray-box testing : It is a blend of whitebox and black-box testing, also known as semi-transparent testing. In this type of testing, the testers are not completely aware of the application internals, functionality, and design requirements. Gray-box testing covers different types of testing like matrix testing, pattern testing, orthogonal pattern testing, and regression testing.
• Code Coverage Techniques : Code coverage is a crucial aspect of unit testing, ensuring that a significant portion of the codebase is tested. Techniques like Statement Coverage, Decision Coverage, and Branch Coverage help in identifying untested parts of the code, thereby improving the effectiveness of unit testing.

Unit testing forms the foundation for the testing process, preceding integration testing. While integration tests assess the overall functionality of the end product, unit tests concentrate on validating individual components within the software system. Although unit tests may not cover every aspect of the software's functionality, they serve as a swift and efficient method for identifying errors. This rapid execution allows for an increased volume of tests in a shorter span. These tests are typically scripted within a separate testing framework, ensuring their independence from the application itself.

Integration testing is ideal to ensure that all application pieces work together correctly. It involves running your entire application under realistic conditions and ensuring that all components work as expected. This type of testing is often used to ensure that no bugs are introduced when integrating new features into existing applications.

Integration testing is a more comprehensive form of testing that tests both the functionality of your components and their interaction with one another.

Here’s a detailed comparison between Unit and integration testing.

Earlier, Unit testing of an application was done manually, which was a time-consuming and cumbersome task. However, test automation has made it easier to automate manual approaches to perform test quickly. To automate unit tests, devs and testers leverage some of the best Unit testing frameworks to test the web app’s components.

Here are some of the most widely used and compatible frameworks you can employ for testing individual components.

• Offers a zero-configuration testing experience, which means you do not have to spend time configuring its environment.
• Comes with easy installation setup and simple mock functions.
• Compatible with Node, React, Angular, Vue, and more.
• The snapshot feature makes it easier to keep track of large objects.

Why Use Jest? : Ideal for developers working on large JavaScript projects, especially in React, looking for a tool that offers a comprehensive testing solution.

• Extremely fast as it has no external dependencies.
• No Document Object Model (DOM) is required.
• Supports both front-end and browser tests.
• It has an active community that provides substantial support and documentation.

Why Use Jasmine? : Jasmine is ideal for JavaScript testing with its behavior-driven approach, enhancing code readability and maintainability across various environments and tools.

Unlock the essence of Unit Testing in Java with this informative video tutorial.

• It implements test-driven development.
• Allows easy integration with build tools like Gradle, Maven, and more.
• Compatible with all popular IDEs.
• Has a simple framework for writing automated tests and self-verifying tests.

Why Use JUnit? : It's ideal for developers looking for a robust, community-supported framework that seamlessly integrates with Java development workflows.

• Easy to understand annotations and grouping of test cases.
• Supports data-driven testing and generates detailed HTML reports.
• Supported by various tools like Maven, Eclipse, and more.
• Allows developers to set priorities for unit tests and run parallel tests.

Why Use TestNG? : Java developers seeking an advanced framework that goes beyond JUnit will find TestNG's extended capabilities highly beneficial.

• Easy to use, needs no configuration or installation.
• Generates instant reports and can create XML reports.
• Allows you to build customized test runners.

Why Use PyUnit? : It's Python's default testing framework, offering simplicity and compatibility with the Python ecosystem.

• Supports all types of testing, including functional, API, UI, database, and more.
• Its intuitive syntax makes it easy to learn.
• Test parallel execution and integration with third-party plugins.

Why Use Pytest? : For Python developers, Pytest offers an intuitive and straightforward approach to both simple and advanced testing needs.

• Supports behavior-driven development (BDD).
• Flexible and accurate reporting.
• Works well with other libraries like Chai for assertions.

Why Use Mocha? : It's perfect for developers who need a flexible and versatile tool for testing JavaScript applications, especially with asynchronous operations.

• Straightforward and extensible API.
• Suitable for both small and complex projects.
• Clear and concise syntax for writing tests.

Why Use QUnit? : It's particularly well-suited for projects that require a lightweight yet robust testing solution.

Unit tests are fast and easy to write, run, and debug — but that doesn't mean you should skip them altogether. Unit tests can take time to set up, especially if they're not automated, so it's important to find ways to speed up their creation, according to most DevOps principles.

You can perform it in two ways:

• Manual : It involves executing each stage of the test manually. Since manual testing is carried out without any automation tool, it's time-consuming and tedious, especially for repetitive test cases, and requires more effort to develop and run test cases.
• Automated : It involves automating repetitive manual tasks using automated testing tools. With tools for automated testing, you can record, save and replay your tests without manual effort.

However, when you test a website, many issues might be unrevealed related to usability. For example, specific functionality of your website works fine on Chrome 99 (Windows 11) but doesn’t work on Firefox 97 (Windows 11). This makes cross browser testing extremely important to fix such usability issues before your customer finds them.

You can utilize various Unit test frameworks to perform automated browser testing and UI testing . A cloud-based testing platform like LambdaTest offers you a scalable cloud to automate your browser and app testing across 3000+ real browsers, devices, and operating systems combinations. It also offers parallel testing to shorten your overall test execution time by multiple folds.

You can subscribe to the LambdaTest YouTube Channel and stay updated with the latest tutorials around automation testing , Cypress UI testing , Responsive testing, and more.

Here are some primary limitations:

• It is not ideal for UI testing, as they are very complex.
• It cannot and will not detect all the errors like integration, interface, or system-wide issues.
• Writing quality tests is challenging and takes a lot of time.
• Every execution part cannot be analyzed.
• It only tests functional attributes.
• Unit tests should be written before any other type of test. If you have specific requirements for your application, you can write a unit test for that functionality. Before implementing them in your code base, you should write tests for any public interface (API) methods.
• Write the test first, then write the code that produces it because your test will give you more information about improving your code.
• Unit tests should be done alongside development rather than afterward. It should also be done more frequently to detect early issues and enhance the quality of the code
• While writing unit tests to speed up your testing process and make your code more flexible and reusable without affecting its performance or stability.

Here are a few tips that you can follow to get the most out of Unit testing:

• The first step is choosing the right tools. It can help you along the process.
• Testing is not a one-time thing, so often, test to ensure your code works correctly.
• Use automated tools instead of manual tools to speed up the process.
• Write simple tests to keep the development code complexity low and test one code at a time.
• Implement some good unit test method name conventions to ensure it is easy to read and understand for your team and conveys what it is about.
• Lastly, make sure your tests are simple, clear, fast-testing structured, reliable, and have clear outcomes. Otherwise, it defeats the purpose of Unit testing.
• It divides your test methods into three sections: arrange, act, and assert. Also, avoid using logical conditions in tests, increasing the chances of bugs. It’s also important to note that unit tests should not contain any logic that directly interacts with other parts of the program but should instead interact only with their functionality.
• Always use fixed values to avoid the fuzz. If you know the input and the output, it becomes a lot more debuggable

In a nutshell

Unit testing is a cornerstone of software development, and it should be part of every developer's toolkit. By creating automated tests for your code, you can ensure that it works properly and will continue to work correctly in the future

If other developers use the software you build, their code will run more smoothly if they know you've already ensured that things will “work as expected.” It keeps bugs from escaping into production, something you don't want as developers or users.

Even better, It isn't as complicated or time-consuming as many believe. And it can be a wonderful learning experience for anyone with a passion for programming who wants to understand their code better.

Delve into our top Unit Testing Interview Questions guide, designed to help you excel in interviews. It covers a wide range of topics, from syntax to advanced techniques, with detailed solutions.

What is Unit testing and its types?

Unit Testing involves validating individual components or modules of a software application. It is carried out during the development phase of an application. It is of two types: manual and automated.

Why do we use Unit testing?

Unit testing is regarded as the first level of testing for validating websites and web applications. Therefore, if you write any code, you must test it before making it live for the general public to ensure they are working as intended.

What is unit testing?

Unit testing is a software testing technique where individual components or units of code are tested in isolation to ensure they function correctly. It focuses on verifying the behavior of small, independent parts of the software.

How to do unit testing?

To perform unit testing, write test cases that target specific units of code, typically using a unit testing framework like Pytest or JUnit. Execute the test cases, validate the expected behavior, and compare it with the actual output.

Why is unit testing important?

Unit testing is essential because it helps detect bugs early in the development process, promotes code quality and maintainability, provides confidence in code changes, and facilitates better collaboration among developers.

What is mock in unit testing?

In unit testing, a mock is an object that simulates the behavior of a real object or component that the code being tested depends on. Mocks allow you to control and verify interactions with dependencies to isolate and test specific code units.

What is unit testing in Python?

Unit testing in Python involves using testing frameworks like unittest or pytest to write test cases that verify the functionality of individual units of Python code, such as functions, classes, or modules.

Who performs unit testing?

Unit testing is primarily performed by software developers themselves as they write the code. They create test cases to validate the behavior of their code units and ensure they work as expected in isolation before integrating them into larger systems.

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Salman Khan

Salman works as a Digital Marketing Manager at LambdaTest. With over four years in the software testing domain, he brings a wealth of experience to his role of reviewing blogs, learning hubs, product updates, and documentation write-ups. Holding a Master's degree (M.Tech) in Computer Science, Salman's expertise extends to various areas including web development, software testing (including automation testing and mobile app testing), CSS, and more.

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• Case report
• Open access
• Published: 28 June 2024

Diagnosis and management of COVID toes in outpatients: a case report

• Marie Pouxe 1 ,
• Aziz Abdulkarim 1 ,
• Serge de Vallière   ORCID: orcid.org/0000-0001-9394-629X 1 , 2 ,
• Teofila Seremet   ORCID: orcid.org/0000-0002-3789-6256 3 ,
• Bernard Favrat   ORCID: orcid.org/0000-0001-6920-099X 1 &
• Ioannis Kokkinakis   ORCID: orcid.org/0000-0002-0033-0988 1  

Journal of Medical Case Reports volume  18 , Article number:  307 ( 2024 ) Cite this article

133 Accesses

Metrics details

Since the beginning of the coronavirus disease 2019 pandemic, the most common skin lesions observed due to infection with the severe acute respiratory syndrome coronavirus 2 are pseudochilblains (or coronavirus disease toes). However, this pathology remains infrequent and difficult to diagnose, as no specific test exists.

Case presentation

Two Caucasian women, 30 and 22 years old, presented to our General Medicine Unit with perniosis lesions on the feet during the first two waves of the coronavirus disease 2019 pandemic. They did not have respiratory or general symptoms of severe acute respiratory syndrome coronavirus 2 infection, the reverse transcription polymerase chain reaction on nasopharyngeal swabs was negative, and the serology was positive only in the first case. The clinical presentation differed for the two cases, as the second patient suffered from swelling and burning after cold application. The diagnosis was based on clinical presentation, temporality, exclusion of other differential diagnoses, and blood test results (positive serology in the first case and high level of CXCL13 and VEGF in the second), supported by current literature. Lesions resolved spontaneously in the first patient. The second case was hospitalized for pain management and received corticosteroid therapy with resolution of the symptoms.

These two cases with different clinical presentations illustrate the diagnostic approach to coronavirus disease 2019, a challenging disease with diverse manifestations, including, in some cases, coronavirus disease toes. We present a literature review that illustrates the progression of scientific research. Skin lesions associated with coronavirus disease 2019 infection could be the expression of an important interferon type 1 response and should be considered in the differential diagnosis in a primary care setting.

Peer Review reports

In December 2019, a new virus was identified in Wuhan, China, called severe acute respiratory syndrome coronavirus (SARS-CoV2-). The virus spread rapidly worldwide, and the World Health Organization (WHO) declared this outbreak a pandemic on 12 March 2020 [ 1 ]. At the onset of the pandemic, COVID-19 infection was described as pneumonia that could induce respiratory failure. Epidemiological studies showed that the most frequent symptoms were fever, malaise, fatigue, cough, sputum, and dyspnea [ 2 ]. Other common symptoms included neurological symptoms, myalgia, diarrhea, headache, rhinitis, and chest pain [ 3 ]. In addition, an abnormally high number of skin lesions associated with COVID-19 were described [ 4 ].

Pseudochilblains, also called pernio or COVID toes, are the most common skin manifestations of COVID-19 disease [ 5 ]. They are mainly described in Europe and the USA but are rarely reported in Asia [ 6 ]. Depending on the studies, the prevalence of pseudochilblains in suspected or confirmed patients with COVID-19 ranges from 3.7% to 29% [ 4 , 7 ]. The prevalence of any skin lesion in suspected or confirmed COVID-19 patients was 60%, of which 48% were pseudochilblains [ 4 ]. In a study with patients with confirmed COVID-19 suffering from skin lesions, the prevalence of pseudochilblains was 30% [ 8 ].

Lesions appear as acral inflammatory erythematous–violaceous macules or papules that can sometimes become blisters or swelling [ 9 ]. Clinical presentation and pathologic features are similar to idiopathic and autoimmune-related chilblains, without the same epidemiologic characteristics (no cold exposure or autoimmune disorder) and are thus called “pseudochilblains” [ 10 ]. Patients frequently show no or few symptoms of COVID-19 before or during pseudochilblains lesions, and biological tests are often negative, making it difficult to prove a link between the skin lesions and the infection. As scientific progress is being made, literature shows evidence of this link [ 11 ].

In this article, we present two cases of COVID toes, which we observed in our emergency department in Lausanne, Switzerland, during two different local waves of COVID-19.

A 30-year-old Caucasian woman presented at the beginning of the SARS-CoV-2 pandemic with foot lesions. She complained of erythematous swelling and a burning sensation on the left foot that had started at T  = 0, initially limited to the third and fourth toes and then progressed to other toes and increased in intensity. At T  = 10 days, she developed blisters, which evolved into desquamation with a diminution of the erythema. The patient complained of tiredness but had no fever or other systemic symptoms during this period. She had no relevant past medical history or family disease.

During the clinical evaluation at T  = 1 month, we noticed a desquamation of several toes without pain, swelling, or redness. Complete blood count and C-reactive protein were normal. A reverse transcription polymerase chain reaction (RT–PCR) test for SARS-CoV-2 on a nasopharyngeal swab was not performed due to the delay since the onset of symptoms and the absence of respiratory manifestations. The SARS-CoV-2 serology at T  = 1 month showed a weak positive IgM level at 2.58 g/L (normal value < 2.41 g/L). A biopsy was not performed, as no skin lesions were found on examination. We retained the pseudochilblain diagnosis based on current literature supporting clinical diagnosis during the COVID-19 outbreak and after excluding other differential diagnoses [ 12 ]. Symptoms resolved spontaneously without treatment within T  = 2 months.

Second case

A 22-year-old Caucasian woman with no other comorbidities ans not vaccinated against COVID-19 presented in the second year of the SARS-CoV-2 pandemic with acute foot lesions without fever or other systemic manifestations. She reported redness, heat, swelling, and itching of all toes associated with pain at T  = 0 (Fig.  1 ). The symptoms were constant, relieved by cold and worsened by heat. She described the appearance of a nodule on the right second toe that lasted for a few days (Fig.  2 ). Dark red punctiform lesions appeared on some toes. During the examination at T  = 5 days, she declared that she was not relieved by topical and oral anti-inflammatory drugs, paracetamol, or antihistamine medication.

Initial clinical presentation of chilblain-like lesions ( T  = 0). Diffuse redness macules and slight swelling of the toes as initial clinical presentation

Evolution two days after the onset of symptoms ( T  = 2 days). A purpuric lesion appeared on the second right toe. Improvement of diffuse redness and edema

The SARS-CoV-2 RT–PCR on nasopharyngeal swabs at T  = 5 and T  = 45 days were negative. At T  = 3 weeks, the toe edema temporarily subsided. A few days later, inflammatory swelling of the two feet reappeared with a burning sensation and diffuse dysesthesia. Other dark red lesions, punctiform or linear, appeared on the back of the two feet (Fig.  3 ), which became crusted.

Evolution 1 month after the onset of symptoms ( T  = 1 month). Inflammatory swelling of the two feet with dark red lesions, punctiform or linear, on the back of the two feet

The patient was finally hospitalized for better pain management at T  = 6 weeks. Clinical examination revealed warm, erythematous edema of both feet and ankles, spreading upwards over both legs’ lower third. There were dark red, punctiform, or linear lesions on the toes and back of the feet. A cyanotic border surrounded some lesions; others were cracked and had a crusty or fibrinous background (Fig.  4 ). The rest of the examination showed a slight decrease in pallesthesia (7.5/8), probably related to edema. A screening for autoimmune diseases and a SARS-CoV-2 serology were negative. The CXCL13 chemokine was elevated at 1021 pg/ml (normal value < 114 pg/ml), and VEGF-A was slightly increased at 663 pg/ml (normal value < 569 pg/ml). Magnetic resonance imaging (MRI) of the feet and ankles showed tenosynovitis of the long extensor digitorum tendons of the right foot, possibly secondary to adjacent tissue compression and fatty infiltration of the dorsum of both feet. Following a dermatological assessment, a skin biopsy was not performed due to extensive swelling.

Evolution after 6 weeks after the onset of symptoms ( T  = 6 weeks). Erythematous edema with dark red, punctiform, or linear crusted lesions on the back of the feet

Although the SARS-CoV-2 RT–PCR and serologies were negative, we retained the pseudochilblain diagnosis after excluding other differential diagnoses and considering COVID toes as a clinical diagnosis during a COVID-19 outbreak following the current literature [ 12 ]. The patient's skin lesions resembled those described in literature in association with waves of COVID-19, and we found an increase of CXCL13 chemokine in the blood, which was related to severe COVID-19 infection [ 13 ]. The diagnosis of erythromelalgia was considered unlikely due to the nonparoxysmal nature of the symptoms.

Symptoms improved significantly after a few days of oral prednisone therapy, 40 mg per day, followed by 20 mg per day for 7 days and 10 mg per day for 7 days. The patient was also treated with pregabalin and tramadol for pain relief and 300 mg of aspirin per day. The pain resolved in a few weeks, she stopped taking painkillers, and the lesions did not recur at T  = 1 year (Fig.  5 ).

Evolution 1 year after the onset of symptoms ( T  = 1 year). No redness or swelling. There are still residual marks from the crusts on the back of the left foot

These two cases of COVID toes had different clinical presentations and evolution, but they both developed symptoms during pandemic waves within a context of high COVID-19 infection incidence, indicating a temporal link. We retained the diagnosis of pseudochilblains or COVID toes based mainly on clinical elements after excluding other differential diagnoses and following current literature for indirect evidence of this association during the COVID-19 outbreak.

The first patient presented typical symptoms and recovered within 1 month. Serology revealed positive IgM for SARS-CoV-2 without positive IgG at T  = 1 month. Studies have shown that antibody titers appear related to disease severity, and a low or undetectable IgG rate might be related to a strong viral clearance [ 14 ].

The second patient had different interesting features of COVID toes, with swelling and a burning sensation after cold application. Although the patient had a negative serology, current literature has shown that an excessive interferon-alpha (IFN-α) response might clear the virus before humoral immunity occurs and explain the negative serology [ 15 ]. Furthermore, the second patient had a high level of CXCL13, which has been shown to be a marker of COVID-19 severity [ 16 ], and a high level of VEGF-A, an endothelial marker, that has been found in late pseudochilblains 20 days after symptom onset [ 17 ]. The evolution was slow over about 2 months and required corticosteroid therapy.

COVID toes occur mainly in children and young adults, last on average 14 days (up to 1 month) and resolve spontaneously. Despite the frequent absence or low-grade typical COVID-19 symptoms, recent contact with COVID-19 patients is often found. The skin lesions occur 2 to 4 weeks after the initial manifestation [ 18 ]. These lesions are primarily associated with mild COVID-19 with a good prognosis [ 19 ]. Laboratory tests are often negative. A study found 7% positive tests without distinguishing RT–PCR or serologies [ 19 ]. In another study, 30% of patients had positive serologies without positive RT–PCR [ 15 ]. Finally, some authors showed negative IgG with positive IgA in children in 31.6% of patients [ 20 ]. The prevalence of these lesions is not known with certainty, but it has been estimated to be between 3.7% and 29% of patients with suspected or confirmed COVID-19 [ 4 , 7 ].

The formal causal link between pseudochilblains and COVID-19 remains challenging to prove. The characterization of this syndrome relies primarily on retrospective studies with many limitations, and the RT–PCR or serologies are often negative [ 20 ]. The RT–PCR is negative in most patients, probably because pseudochilblains appear late during the infection. It has also been shown that patients with COVID-19 with mild or no symptoms have lower viral loads that are more challenging to detect [ 15 ]. Also, we currently know that specific early humoral response to SARS-CoV-2 is dominated by IgA, which has a crucial role in virus neutralization. Serologies might be negative because IgA is not analyzed in routine serology [ 21 , 22 ]. At last, as mentioned above, this could be related to a strong IFN-α response that clears the virus before the humoral response [ 15 ].

Type 1 IFN is known as essential for host defense against viruses and a high concentration of type 1 interferon-inducible myxovirus resistance protein A has been found in pseudochilblain biopsies, similar to the transcriptional signature of lupus [ 23 ]. Therefore, some people would have a strong type 1 IFN response that would favor rapid elimination of the virus without suffering from the disease, thus blocking seroconversion. Pseudochilblains would, therefore, be a viral-induced type I interferonopathy [ 24 ]. A study has identified a stimulator of interferon genes (STING)-dependent type I IFN signature that is primarily mediated by macrophages adjacent to areas of endothelial cell damage [ 25 ].

A recent review proposes that the mechanism of COVID toes is related to an interaction between SARS-CoV-2 cell infection via ACE2, the RAAS (renin–angiotensin–aldosterone system), sex hormones, and the IFN type I immune response [ 26 ]. In a small case series, viral particles were found in endothelial cells, suggesting that the vessel damage could be directly related to SARS-CoV2 [ 27 ]. Finally, one study compared idiopathic chilblains to pseudochilblains, demonstrating histological similarities. However, pseudochilblains showed a systemic response with a high prevalence of ANCA, IgA, and IFN type 1 and an endothelial alteration [ 17 ].

Pseudochilblain or COVID toes is a recent disease that emerged with the COVID-19 pandemic. Current literature suggests pathophysiological mechanisms related to a cutaneous expression of an important IFN type 1 response. The typical clinical presentation, history, and examination, the consideration and exclusion of other differential diagnoses, the absence of a history of perniosis, and the timing of COVID waves allow the diagnosis of pseudochilblains following a COVID-19 infection. Clinicians in primary care should be aware of chilblain-like lesions and suspect COVID-19 infection, even in the presence of a negative RT–PCR test and negative serology.

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Muralidar S, Ambi SV, Sekaran S, Krishnan UM. The emergence of COVID-19 as a global pandemic: understanding the epidemiology, immune response and potential therapeutic targets of SARS-CoV-2. Biochimie. 2020;179:85–100.

Article   CAS   PubMed   PubMed Central   Google Scholar  

Wu D, Wu T, Liu Q, Yang Z. The SARS-CoV-2 outbreak: What we know. Int J Infect Dis. 2020;94:44–8.

da Rosa Mesquita R, Francelino Silva Junior LC, Santos Santana FM, Farias de Oliveira T, Campos Alcântara R, Monteiro Arnozo G, et al . Clinical manifestations of COVID-19 in the general population: systematic review. Wien Klin Wochenschr. 2021;133:377–82.

Perna A, Passiatore M, Massaro A, Terrinoni A, Bianchi L, Cilli V, et al . Skin manifestations in COVID-19 patients, state of the art A systematic review. Int J Dermatol. 2021;60:547–53.

Jimenez-Cebrian AM, Castro-Mendez A, García-Podadera B, Romero-Galisteo R, Medina-Alcántara M, Garcia-Paya I, et al . Clinical manifestations of COVID-19 in the feet: a review of reviews. J Clin Med. 2021;10:2201.

Tan SW, Tam YC, Oh CC. Skin manifestations of COVID-19: a worldwide review. JAAD Int. 2021;2:119–33.

Article   PubMed   Google Scholar  

Mascitti H, Jourdain P, Bleibtreu A, Jaulmes L, Dechartres A, Lescure X, et al . Prognosis of rash and chilblain-like lesions among outpatients with COVID-19: a large cohort study. Eur J Clin Microbiol Infect Dis. 2021;40:2243–8.

Giavedoni P, Podlipnik S, Pericàs JM, Fuertes de Vega I, García-Herrera A, Alós L, et al . Skin Manifestations in COVID-19: prevalence and relationship with disease severity. J Clin Med. 2020;9:3261.

Kashetsky N, Mukovozov IM, Bergman J. Chilblain-Like Lesions (CLL) Associated With COVID-19 (“COVID Toes”): A Systematic Review. J Cutan Med Surg. 2021;120347542110045.

Kanitakis J, Lesort C, Danset M, Jullien D. Chilblain-like acral lesions during the COVID-19 pandemic (“COVID toes”): Histologic, immunofluorescence, and immunohistochemical study of 17 cases. J Am Acad Dermatol. 2020;83:870–5.

Feito-Rodríguez M, Mayor-Ibarguren A, Cámara-Hijón C, Montero-Vega D, Servera-Negre G, Ruiz-Bravo E, et al . Chilblain-like lesions and COVID-19 infection: a prospective observational study at Spain’s ground zero. J Am Acad Dermatol. 2021;84:507–9.

Kolivras A, Thompson C, Pastushenko I, Mathieu M, Bruderer P, Vicq M, et al . A clinicopathological description of COVID ‐19‐induced chilblains ( COVID ‐toes) correlated with a published literature review. J Cutan Pathol. 2021;cup.14099.

Alturaiki W, Alkadi H, Alamri S, Awadalla ME, Alfaez A, Mubarak A, et al . Association between the expression of toll-like receptors, cytokines, and homeostatic chemokines in SARS-CoV-2 infection and COVID-19 severity. Heliyon. 2023;9: e12653.

Article   CAS   PubMed   Google Scholar  

Tan W, Lu Y, Zhang J, Wang J, Dan Y, Tan Z, et al . Viral Kinetics and Antibody Responses in Patients with COVID-19. Infect Dis (except HIV/AIDS); 2020. https://doi.org/10.1101/2020.03.24.20042382

Hubiche T, Cardot-Leccia N, Le Duff F, Seitz-Polski B, Giordana P, Chiaverini C, et al . Clinical, laboratory, and interferon-alpha response characteristics of patients with chilblain-like lesions during the COVID-19 pandemic. JAMA Dermatol. 2021;157:202.

Perreau M, Suffiotti M, Marques-Vidal P, Wiedemann A, Levy Y, Laouénan C, et al . The cytokines HGF and CXCL13 predict the severity and the mortality in COVID-19 patients. Nat Commun. 2021;12:4888.

Frumholtz L, Bouaziz J ‐D., Battistella M, Hadjadj J, Chocron R, Bengoufa D, et al . Type I interferon response and vascular alteration in chilblain‐like lesions during the COVID‐19 outbreak. Br J Dermatol. 2021;bjd.20707.

Gisondi P, Di Leo S, Bellinato F, Cazzaniga S, Piaserico S, Naldi L. Time of onset of selected skin lesions associated with COVID-19: a systematic review. Dermatol Ther. 2021;11:695–705.

Article   Google Scholar  

Freeman EE, McMahon DE, Lipoff JB, Rosenbach M, Kovarik C, Takeshita J, et al . Pernio-like skin lesions associated with COVID-19: A case series of 318 patients from 8 countries. J Am Acad Dermatol. 2020;83:486–92.

El Hachem M, Diociaiuti A, Concato C, Carsetti R, Carnevale C, CiofiDegliAtti M, et al . A clinical, histopathological and laboratory study of 19 consecutive Italian paediatric patients with chilblain-like lesions: lights and shadows on the relationship with COVID-19 infection. J Eur Acad Dermatol Venereol. 2020;34:2620–9.

Article   PubMed   PubMed Central   Google Scholar  

Lippi G, Mattiuzzi C. Clinical value of anti-SARS-COV-2 serum IgA titration in patients with COVID-19. J Med Virol. 2021;93:1210–1.

Mathian A, Sterlin D, Miyara M, Mohr A, Anna F, Quentric P, et al . Les Immunoglobulines A dominent la réponse anticorps neutralisante précoce anti-SARS-CoV-2. Rev Médecine Interne. 2020;41:A63–4.

Magro CM, Mulvey JJ, Laurence J, Sanders S, Crowson AN, Grossman M, et al . The differing pathophysiologies that underlie COVID-19-associated perniosis and thrombotic retiform purpura: a case series. Br J Dermatol. 2021;184:141–50.

Yatim A. Gilliet M [COVID-toes, a cutaneous sign of innate resistance to SARS-CoV-2]. Rev Med Suisse. 2021;17:646–52.

PubMed   Google Scholar  

Domizio JD, Gulen MF, Saidoune F, Thacker VV, Yatim A, Sharma K, et al . The cGAS–STING pathway drives type I IFN immunopathology in COVID-19. Nature. 2022;603:145–51.

Cappel MA, Cappel JA, Wetter DA. Pernio (Chilblains), SARS-CoV-2, and COVID toes unified through cutaneous and systemic mechanisms. Mayo Clin Proc. 2021;96:989–1005.

Colmenero I, Santonja C, Alonso-Riaño M, Noguera-Morel L, Hernández-Martín A, Andina D, et al . SARS-CoV-2 endothelial infection causes COVID-19 chilblains: histopathological, immunohistochemical and ultrastructural study of seven paediatric cases. Br J Dermatol. 2020;183:729–37.

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MP drafted the case reports, reviewed literature, and wrote the manuscript. AA cared for one patient and revised the manuscript. BF cared for one patient and revised the manuscript. TS and SDV revised the manuscript as dermatology and infectious diseases consultants. IK reviewed the literature, revised and supervised the manuscript, and was the correspondace author. All authors read and approved the final manuscript.

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Pouxe, M., Abdulkarim, A., de Vallière, S. et al. Diagnosis and management of COVID toes in outpatients: a case report. J Med Case Reports 18 , 307 (2024). https://doi.org/10.1186/s13256-024-04626-9

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