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Last updated September 9, 2021. 8 minute read

How does a mouth swab COVID-19 test work?

You may have seen claims circulating that mouth swab tests are less reliable than nasal swabs. But the story is a little more complicated than that. We’ve covered everything you need to know about mouth swab COVID tests, how they work, how reliable they are and when to get one.

Linnea Zielinski Written by Linnea Zielinski
Reviewed by Yael Cooperman, MD

Getting tested for coronavirus disease 2019 (COVID-19) can be overwhelming, even if you’ve already been tested before. But testing should be something that alleviates stress, not causes it. 

Still, there is so much constantly evolving information about COVID-19 testing that it can feel like you need to be a medical professional to even know where to turn 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.


  • To find out if you have COVID-19, there are a few tests you can take including mouth swabs, nose swabs, and saliva tests. During a mouth swab test, you use a cotton swab to collect a sample from inside your mouth. It’s different from a saliva test, where you spit into a small container.

What types of COVID-19 tests are there?

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

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

Both of these tests use nose or mouth swabs. PCR tests can also be done using saliva (FDA, 2021-a). The saliva and mouth swab tests sound like the same thing, but they’re not. What’s the difference? 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 a 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.

You may have also heard of antibody tests. These tests look for antibodies, which your immune system makes after it encounters an invader like the coronavirus or after it responds to a vaccine. 

Antibody tests are typically done using a blood sample. Unlike antigen tests, they can’t tell you if you currently have COVID-19. Instead, these tests tell you if you were infected with COVID-19 in the past. An antibody test can also show if you’ve been vaccinated.

Which COVID-19 test is most reliable?

What type of COVID-19 test you get usually depends on where you live, and what’s available.

You may have seen claims circulating that mouth swab tests are less reliable than nasal swabs. But how is that measured? No matter the type, the accuracy of all COVID-19 tests is described in terms of sensitivity and specificity, which refers to how accurately the tests identify the virus in your system (Swift, 2020). For example, a test that has 97% sensitivity can accurately identify 97 out of 100 COVID-19 cases. However, in the other three cases, it will give false negatives, meaning it says you don’t have COVID-19 even though you do.

Molecular tests like PCR are generally considered to be the most accurate COVID-19 tests (Nagura-Ikeda, 2020). However, PCR tests take longer than rapid antigen tests and require special machinery. This means they have to be done in a lab and you don’t get your results right away.

Antigen tests might not be quite as good at identifying every case of COVID-19, but tests that come back positive are extremely accurate. You may need a PCR test if your antigen test comes back negative, though, especially if you have a known exposure to a person who tested positive or if you have symptoms of COVID-19 (FDA, 2021-a). Different antigen tests have different accuracy, but one test studied can accurately identify 80 out of 100 cases of COVID-19 when people have symptoms and 40 out of 100 cases when people have no symptoms (Pray, 2021).

Why do some tests have false negatives?

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. This can happen early on in the infection—often before you even develop symptoms. It can take between two and 14 days to develop symptoms of COVID-19 from the time you were exposed (CDC-f, 2021). Early on in the infection, you might have very little 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. You could have a small amount of virus, just not enough to appear on a test yet. And even if you tested negative before, you could still catch COVID-19 at the gas station or any other stop on the way to visit family or friends. This is why it’s important to practice social distancing, avoid going out without a mask covering your nose and mouth, and avoid spending time with people who aren’t part of your household until you are fully vaccinated (CDC, 2021-b). 

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, 2020-b). Your healthcare provider will take into account 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 20 and 31% of people with COVID-19 will be asymptomatic the entire time they’re sick (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, you may be asked to remain home and isolate rather than leave the house to get tested and potentially expose other people to COVID-19. 

Before you start visiting with people outside of your household it’s important 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. Once you’re fully vaccinated, you can even visit with other vaccinated people, according to the CDC.

How to do a mouth swab COVID-19 test

There are different ways the mouth swab COVID-19 test may be done:

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

You may need to take certain steps before the test to make sure 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 be reminded 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 lungs, and preliminary research suggests this improves the chance of identifying coronavirus in samples (Kojima, 2020).

If someone is administering the test, they will swab the inside of your mouth. If it’s a self-collection test, you’ll have a sheet with instructions outlining the process.

Where to get a mouth swab COVID-19 test

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. People who have taken part in any activity that puts them at a higher risk for COVID-19 because they cannot socially distance themselves should also get a test done. That includes travel, large get-togethers, or crowded indoor settings (CDC, 2021-d).

If you’re unsure whether you need to get tested, you can use the CDC’s self-checker tool (CDC, 2021-e).

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, 2020-a).

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, 2020-b; FDA, 2020-c).

Some pharmacies offer access to COVID-19 tests, but most offer nose swab tests instead of 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 (CVS, n.d.). Rite Aid and Walgreens offer similar services (Rite Aid, n.d., Walgreens, n.d.). Quest Diagnostics also offers testing at select Walmart locations (Quest Diagnostics, n.d.).


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