Experts explain why you shouldn't brush off your nail biting habit.

Onychophagia, or nail biting, is a pretty common habit. About half of all pre-teens and teens bite their nails, according to health experts at the University of Michigan, though most people stop after the age of 30 (or at least stop admitting to it). Nail biting—which can be caused by stress, anxiety, obsessive-compulsive disorder, or just being bored and fidgety—may seem perfectly harmless, but it can invite bacteria, viruses, or fungi to enter into the body and bloodstream, increasing your chances of catching a nasty infection—including the new coronavirus. “Nail biting is very risky right now as we know the virus can live on surfaces, such as your nails, and is most commonly transmitted to your face by touching your face,” says Purvi Parikh, MD, adult and pediatric immunologist and an allergist at NYU Langone Health in New York City. “So if you are biting your nails you are risking ingesting not only the virus, but other bacterial and viral pathogens.” (Check out these 7 annoying habits—here’s why we can’t help it.)

How bad is it to bite your nails?

How nail biting leads to bacterial and fungal infections

If you’ve ever had a manicure, you’ve no doubt noticed the gunk that the manicurist removes from under your nails. That’s what you can see with the naked eye—so just imagine all the bacteria you can’t see. The most common pathogens lurking under our nails are Staphylococcus, Streptococcus, and Coryneform bacteria, which can enter the body through breaks in our skin or—you guessed it—from ingesting them after biting your nails.

If that isn’t enough of a deterrent, just imagine dermatophyte fungi, also known as ringworm, hanging out in your nail tissue as you open mouth and insert finger. “Ideally nails should be kept short, and frequent hand washing should occur,” says Dr. Parikh, echoing the recommendations of the Centers for Disease Control and Prevention (CDC). According to the CDC, clean hands are the single most important factor in preventing the spread of pathogens and antibiotic resistance in healthcare settings. Next time stress makes you want to bite your nails, try some healthy breathing techniques, instead.

How nail biting leads to cold and flu

According to the CDC, there are more than 200 cold viruses floating around at any given time. Even though the risk factors for acquiring one include a weakened immune system and/or exposure to someone sick, you can significantly reduce your chances of catching a virus by keeping your hands away from “your face, especially your mouth and nose,” says Dr. Parikh. Viruses that cause the flu also flourish on your skin, so wash your hands frequently with soap and water (or use an alcohol-based hand sanitizer), and discourage nail biting by chewing gum. “Keeping nails short is the best deterrent so you are not tempted,” says Dr. Parikh. “Some nail biters report painting their nails with a clear or colored polish that deters nail biting due to the taste.”

How nail biting can harm your teeth

Nail biting can also damage the teeth and gums. Nail biting can crack, chip, or wear down the front teeth, and also potentially lead to sore gums and gum tissue damage. Ask your dentist if a mouthguard could help you to stop biting your nails—or at least minimize some of the damage it can cause. She may also be able to suggest some other techniques to help you quit the habit for good. A study published in 2016 in Case Reports in Dentistry suggests that a fixed oral appliance placed by a dentist may be a solution since it makes nail biting unpleasant and difficult. Next, check out these 10 tips for strong, healthy nails.