Why people bite their nails

Dear Mr. Alice: Why is it that so many people bite their nails? — Michelle, San Diego

It’s been studied scientifically, so there are a few reliable things to say about onychophagia. Unfortunately, “why” is not one of them.

Every time you sit down to a dinner for four, consider that one of you probably had a fingernail hors d’oeuvre sometime that day. (Actually, most nail-biters don’t swallow, they spit when they’re through doing whatever they do with the torn-off nail.) One out of four adults (regardless of sex, national origin, IQ, mental stability) is a nail-biter. And one out of three nail-biters has the inclination (and agility) to bite his or her toenails.

Nail biting usually begins between ages five and six, though peak nail-biting years are, no surprise, adolescence. Studies suggest a predisposition to nail biting is inherited. And many investigators believe the habit’s a way to discharge tension, anxiety, or anger, but nobody’s proved it scientifically. Part of the problem in finding out “why” is the likelihood that nail biting begins as a response to some stimulus but persists into adulthood purely as a long-term habit, years after the stimulus is gone. So adult nail-biters can’t say why they do it, only that they are compelled to.