From Shape Magazine:
Nail biting, technically called onychophagia, may seem innocent enough—in fact, up to 50 percent of us will chronically gnaw our nails at some point in our life, according to a study from the University of Calgary. But experts warn that the nervous habit can have consequences far worse than ruining your pricey manicure. From making you sick to making you look insecure, these 10 science-backed facts are scary enough to make you nix the bad habit for good. (Learn what 7 Things Your Nails Can Tell You About Your Health.)
There's a reason cops and coroners always clean out under a victim's nails on crime shows: Fingernails are perfect catch-alls for dirt and debris. When you chew yours, you're giving all those germs a one-way ticket to your insides, says Michael Shapiro, M.D., medical director and founder of Vanguard Dermatology in New York City. "Your fingernails are almost twice as dirty as your fingers. Bacteria often gets stuck under the nails, and can then be transferred to the mouth, causing infections of the gums and throat."
"Think of every single thing you touch during your day, from doorknobs to toilets," says Kristine Arthur, M.D., an internist at Orange Coast Memorial Medical Center in Fountain Valley, CA. "Germs can live on these surfaces for hours, so when you stick your hands in your mouth, you're exposing yourself to cold and flu viruses, or even serious illnesses like hepatitis." (Learn 6 Ways to Clean Your Place Like a Germ Expert.)
Worse, hangnails are open sores which can easily get infected, Shapiro says. The best way to avoid the painful sores is to prevent the hangnail from forming in the first place by moisturizing regularly—and not chewing on your fingers.
Whether or not the stereotype is true, nail biters often put out a self-conscious vibe. "Most people bite their nails to seek comfort or relief from a negative emotional state, such as distress, shame, anxiety, or boredom," says Mary Lamia, Ph.D., clinical psychologist and professor at the Wright Institute in Berkeley, CA. "In a sense, nail biting attacks the self, which tends to result in publicly exposing one's feelings of shame and of disgust about the self." (Try one of these 15 Easy Ways to Beat Everyday Anxiety instead.)
Facial warts aren't just for wicked witches: "Warts on your fingers can be caused by human papillomavirus, or HPV," Shapiro says. "These warts can easily spread to other fingers, your face, your mouth, and even your lips," adds Arthur.
Biting isn't just bad for your fingers, it's also bad for your teeth. "It can interfere with proper dental occlusion, or the manner in which your upper and lower teeth come together when you close your mouth," Shapiro says. "Plus, your teeth may shift out of their proper position, become misshapen, wear down prematurely, or become weakened over time." (Learn what 11 Things Your Mouth Can Tell You About Your Health.)