You do it while you’re reading emails or watching television; the tip of a finger creeps up between your teeth, and you nibble away for a few minutes before catching yourself. Your mom always told you it was a bad habit, and you worry about coworkers eye-balling your shredded digits. But is biting your fingernails actually dangerous?

“Yes, and for a number of different reasons,” says Richard Scher, M.D., an expert on nail disorders at Weill Cornell Medical College and a member of the American Academy of Dermatology.

To begin with, your nails harbor all sorts of germs. In particular, a family of bacteria called enterobacteriaceae — which includes salmonella and E. coli — tends to thrive in the cozy crevice beneath the tips of your nails, Scher explains. When you bite your nails, those bacteria end up in your mouth and gut, where they can cause gastro-intestinal infections that lead to diarrhea and abdominal pain.

Long-term, habitual nail nibblers can also suffer from a type of infection called paronychia, Scher says. Tears or abrasions in the skin of your fingertips allow strains of bacteria or yeast to get inside. Both cause swelling, redness, and a buildup of puss around and under the nail, which has to be drained surgically and treated with antibiotics or antifungal agents, he explains.

If the infection is bacterial, the nail can also become tender and painful. “You’ll see it where every fingertip becomes inflamed,” Scher adds.

The wart virus HPV is also a common infection among nail biters, says Chris Adigun, M.D., a dermatologist at NYU Langone Medical Center. After infecting the fingers, these warts can then spread to your mouth and lips, Adigun adds.

The perils of nail biting also extend to your teeth. “Constant biting can lead to poor dental occlusion, so the biter’s teeth shift out of position or become oddly shaped,” Scher says. Biters also suffer from higher rates of gum disease and infection, he adds.

So how do you quit the habit? For a lot of people, nail biting is a manifestation of stress or psychological disorders.

“Both tend to cause teeth grinding, and your fingernails are a handy buffer.” You’ll have a hard time stopping without help from a psychiatrist or mental-health professional, he says. If your habit is mild, Scher says there are over-the-counter products you can spread on your nails that have a bitter taste. “The taste reminds you not to bite,” he explains.

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