How does a mouth swab COVID test work?

Getting tested for COVID-19 can be overwhelming, even if you’ve already had a test before. But testing should be something that alleviates stress, not something that causes it. 

Still, there is so much constantly evolving information about COVID testing that it can feel like you need to be a medical professional to even know where to turn to first. If you’re trying to figure out whether to get tested and how it works, we’re here to help. Here’s what you need to know about mouth swab COVID tests and other options for finding out if you have COVID-19.

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When it comes to diagnosing COVID-19, there are two main types of tests usually performed: 

• Molecular tests, like PCR (polymerase chain reaction) tests, which look for the virus’s genetic material

• Antigen tests, which look for the virus’s outer shell

Both of these tests can be done using nose or mouth swabs. PCR tests can also be done using saliva (FDA-a, 2021). While the saliva and mouth swab tests sound like the same thing, they’re actually slightly different. A saliva test requires you to spit into a tube, while a mouth swab test involves rubbing the inside of your mouth with a cotton swab to get the sample. 

Nasal swabs follow the same protocol as mouth swabs, except you or a healthcare professional takes a swab sample from your nose instead of your mouth.

One additional type of test is an antibody test (also known as serology tests). (A good trick for remembering the difference between antibodies and antigens is that antibodies are what your body produces in response to the virus or vaccine.) These won't tell you if you're currently infected but can instead tell you if you've had the infection in the past or if you've been vaccinated. Antibody tests typically require a blood sample.

There are different ways to do a COVID-19 mouth swab:

• A healthcare professional may swab your mouth for you.

• A healthcare professional may supervise while you do it yourself.

• You may be given a kit at a testing location with instructions for how to swab your mouth.

• You can use an at-home mouth swab kit.

You may need to take specific steps before the test so that the results are as accurate as possible. If you need to book an appointment, ask if there’s anything you should avoid on the day of your test. Some types of tests that use saliva require that you don’t eat, drink, smoke, brush your teeth, or chew gum 30 minutes before the test (FDA, 2020).

You may have to cough forcefully 3-5 times and keep the phlegm in your mouth before you swab if a medical professional is conducting or supervising the test. That’s because coughing brings up secretions from your upper airways, and preliminary research suggests this improves the chance of identifying coronavirus in samples (Kojima, 2020).

If you’re currently experiencing symptoms of COVID-19, if you’ve been in close contact (within six feet for 15 minutes or more) with someone with a confirmed case of COVID-19, or if your healthcare provider tells you to do so, you should go get tested (CDC-d, 2021). If you’re unsure whether you need to get tested, you can use the CDC’s self-checker tool (CDC-e, 2021).

If you know you’ve been in close contact with someone with COVID-19 or in a situation that puts you at risk of getting it, you can speak with your healthcare provider, your local urgent care, or your state or local health department to find out where to get tested (CDC-a, 2020).

The U.S. Food and Drug Administration (FDA) has granted emergency use approval for some at-home molecular and antigen tests that don’t require a prescription and can be ordered online (FDA-b, 2020; FDA-c, 2020).

Some pharmacies offer access to COVID-19 tests, but most offer nose swab tests rather than mouth swabs. These tests are just as quick as mouth swab tests. While they can be a little bit uncomfortable, they’re not painful. CVS’s MinuteClinic has a tool for finding a participating location in your area. Rite Aid and Walgreens offer similar services. Quest Diagnostics also offers testing at select Walmart locations.

COVID-19 tests should be sensitive and specific. Sensitivity and specificity are how accurately a test identifies the virus in your system. For example, if there are 100 people with COVID, a test that is 97% sensitive will catch 97 cases. However, the other three cases will be false negatives, meaning it says those people don’t have COVID-19 even though they do.

You may have seen claims circulating that mouth swab tests are not as reliable as nasal swabs. But how is that measured? 

Molecular tests (also known as PCR tests) are often the most accurate COVID-19 tests (Nagura-Ikeda, 2020). However, PCR tests take longer than rapid antigen tests and require special equipment. They must be sent out for processing in a lab, and it can take some time to get your results.

Rapid (antigen) tests might not be quite as good at identifying every case of COVID-19, but when these tests are positive, they're typically accurate. You may need a PCR test if your antigen test comes back negative, though, especially if you have had a known exposure to a person who tested positive or if you have symptoms of COVID-19 (FDA-a, 2021). 

Whether or not you have symptoms can also affect the accuracy of a COVID test. Research has shown that the rapid antigen nasal swab test can accurately identify 80 out of 100 cases of COVID-19 when people have symptoms, but only 40 out of 100 cases among people who are asymptomatic (Pray, 2021).

What is a false negative and why does it happen?

Sometimes tests aren’t accurate. If a person has COVID-19, but the test says they don’t, that's called a false negative. 

A false negative can happen with any type of test but is typically more common if you only have a small amount of the virus in your body. False negatives can occur early on in the infection—often before you even develop symptoms. It can take between two and 14 days from the time you were exposed to develop symptoms of COVID-19, and some people never develop symptoms at all (CDCf, 2021). Early in the infection, you might have a tiny amount of virus in your body, and the test can miss it. 

What happens after I get my test results?

Even if your COVID-19 test comes back negative, it doesn’t mean it’s time to visit your grandparents. 

Results can sometimes be inaccurate, and COVID-19 tests are also just a snapshot of the overall picture. The most important factor when it comes to avoiding infection is getting the vaccine (and the booster, if you're eligible) (CDC-b, 2021). If you've been vaccinated, getting tested is still a good idea if you know you've been exposed to someone who has tested positive. That's because although your risk is reduced, you can still catch and transmit the virus after being fully vaccinated.

Remember: a COVID-19 test result isn’t the final word, even if you are already vaccinated. If you have symptoms of COVID-19 and your test is negative, consult with a healthcare provider about getting another test and consider isolating yourself from the other people in your home (CDC-b, 2021). Your healthcare provider will assess your symptoms and any exposures you might have had when deciding whether or not to send you for another test. 

Not every COVID-19 case requires an in-person evaluation by a healthcare professional. Studies have found that between roughly 20 and 30% of people who catch the coronavirus will be asymptomatic but still able to transmit the virus to others (Buitrago-Garcia, 2020).

According to the World Health Organization, 80% of people with confirmed cases of COVID-19 have mild-to-moderate symptoms (WHO, 2020). If your symptoms remain mild, your provider might advise you to stay home and isolate rather than leave the house to get tested and potentially expose other people to the coronavirus. Before you start visiting with people outside of your household, it's helpful to make sure that you're fully vaccinated. Now that the vaccines are so widely available, it's a lot easier to get your shots. According to the CDC, once you're fully vaccinated, it's safe to resume some of your pre-pandemic activities (CDC-g, 2021).

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

October 22, 2021

Written by

Linnea Zielinski

Fact checked by

Yael Cooperman, MD

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About the medical reviewer

Yael Cooperman, MD, Ro

Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.