For starters, biting your nails can raise the risk of catching a cold or other illness because you’re putting your unwashed hands in your mouth. It can also raise the risk of paronychia, or infection of the skin surrounding the nail, says Rochelle Torgerson, M.D., Ph.D., a dermatologist at the Mayo Clinic.
You can “end up with redness and swelling and pain and discomfort — that’s a sign of infection,” Torgerson tells HuffPost. While most instances of paronychia are bacterial, they can also be fungal.
In addition, if you have a wart, biting your fingernails is a way to raise your risk of spreading warts to other parts of your hands. That’s because warts are caused by one of the many kinds of human papillomavirus (HPV), a virus that spreads as an infection. “The more open skin you have, the more you’re going to spread” the virus, she says.
Biting or picking your nails could also lead to temporary or permanent effects to your actual nail. Torgerson explains that the majority of the fingernail is produced in the area of the nail bed where there is a “white hill,” also called the lunula. The fingernail is made there, as well as the area beneath the lunula that extends down underneath the skin. “So if you end up with a lot of inflammation or an infection of that skin … where the fingernail is made, you can start making a funny fingernail,” she explains. “You may end up with a fingernail that’s bumpy or ridge-y.”