Swabs that come with at-home rapid antigen COVID-19 tests should be used in the nose and not the throat, the U.S. Food and Drug Administration warns.

It issued the warning on Twitter in response to reports that some people are using swabs intended for nasal samples to take samples from their throats and posting their results on social media with the hashtag #SwabYourThroat. The trend began after early research suggested saliva may be a better way to detect the Omicron variant.

"The FDA advises that COVID-19 tests should be used as authorized, including following their instructions for use regarding obtaining the sample for testing," an FDA spokesperson told CNN.

"The FDA has noted safety concerns regarding self-collection of throat swabs, as they are more complicated than nasal swabs -- and if used incorrectly, can cause harm to the patient," the spokesperson said. "The CDC recommends that throat swabs be collected by a trained health care provider."

The best thing you can do is to follow the instructions on the test kit, Dr. Emily Volk, president of the College of American Pathologists, told CNN.

"The test is designed for the specimen collection that they describe in the instructions, so any deviation from that, you're not going to get the results that are expected," Volk said.

Throat swabs are common in some countries, but most COVID-19 self-tests in the United States require nasal samples.

It may turn out that throat swabbing is an effective way to gather material for tests, Dr. Sten Vermund, a pediatrician and infectious disease epidemiologist at the Yale School of Public Health, told CNN. "But that data isn't there yet."

Another expert agreed.

"Even if you think you're going to be more likely to detect virus that way, you don't know that," Dr. Graham Snyder, medical director of infection prevention and hospital epidemiology at the University of Pittsburgh Medical Center, told CNN.

"The test won't perform better if you use it in a different way than its instructions say," Snyder said. "We also know from a lot of data throughout the pandemic that swabbing the nose turns out to be pretty good, so I'm not even sure you have to subject yourself to a throat swab."