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The psychology of why so many people bite their nails

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Excessive nail biting is a surprisingly widespread human activity.

It goes back millennia: the ancient Greek philosopher Cleanthes, for instance, was said to be addicted to biting his nails. In the modern era, no one has any good data on how many of us share the affliction (technically called onychophagia), but small-scale studies indicate about 20 percent or so of adults bite regularly — which would suggest millions of Americans do it.

"Everybody picks and bites to a degree," says Fred Penzel, a psychologist who helps patients deal with nail biting, hair plucking, and other body-focused repetitive disorders. "When it gets to the point that people are doing damage to themselves, that's when we treat it as something other than an everyday behavior." This certainly applies to a much smaller number of people — but it's still, he says, a surprisingly common problem.

Even though excessive nail biting is widespread, however, psychologists have only begun studying it within the past few decades. In fact, they're still trying to understand the basic question that many people with onychophagia spend so much time wrestling with: given that the rational part of our brain wants to quit, why do we keep biting our nails?

The current hypothesis: nail biting helps even out our emotions. When we're bored, it provides stimulation; when we're stressed out or frustrated, it provides a temporary calm.

Early theories on why we bite our nails have been rejected

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Most of the early explanations of nail biting have been thoroughly disregarded. Sigmund Freud, for instance, believed that excessive nursing during infancy could lead to a so-called "oral receptive" personality — and a tendency to chew on nails and other objects, as well as a distinct preference for oral sex. He had no evidence for this idea, and subsequent followers of his ideas didn't turn up any, either.

Later, some researchers considered nail biting, hair plucking (called trichotillomania) and skin picking as mild forms of self-harm — the intentional injuring of oneself, often by cutting. Under this theory, biting one's nails would be sign of hostility towards oneself.

Undercutting this idea, however, is the fact that most nail biters aren't particularly fond of the damage their habit causes — and for many people, it's the main reason they want to quit. Starting in the 1990s, most psychologists began distinguishing it and body-focused repetitive disorders from more severe forms of self-harm.

As they've begun to better understand the behavior, one big question is whether it should be grouped in with obsessive-compulsive disorder (OCD). Though the latest DSM (a text that's considered an authority on psychiatric diagnoses) puts nail biting in a broader category with OCD, many of those who specifically study body-focused repetitive disorders disagree.

"The word 'obsessive' doesn't really apply," says Penzel. "Every behavior that's repetitive is not necessary a compulsion."

Compulsions, for one, are usually associated with extreme levels of anxiety. Nail biting, on the other hand, is often accompanied by pleasure — the people who do it want to do it, except for the fact that it causes damage over time. Though people with OCD appear to have a greater chance of being nail biters, they seem to be distinct disorders.

The new theory: nail biting helps us balance out our emotions

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Recently psychologists have come to a more plausible theory of nail biting: that it can provide a temporary escape, distraction, or bit of pleasure or relaxation for the biter.

Penzel points out that many people get the urge to bite when they're understimulated (i.e., bored) or overstimulated (stressed out or excited). "When they're understimulated, the behaviors provides stimulation, and when they're overstimulated, it actually helps calm them down," he says. Like nicotine, the idea is that nail biting can have a biphasic effect: it can stimulate under certain conditions and relax in others.

It's still not proven, but to someone who's spent a lot of time biting her nails, this explanation rings true — and a recent study conducted by Sarah Roberts and other researchers at University of Quebec at Montreal provides a bit of evidence for it.

In the study, people with onychophagia, trichotillomania, or other body-focused repetitive behaviors were put into situations designed to elicit frustration (they were given a difficult task that couldn't possibly be completed in the allotted time), boredom (they were left in a room with absolutely nothing to do for a while), anxiety (they watched a notoriously terrifying plane crash scene from the movie Alive), or relaxation (they watched a video of a beach from a comfortable chair).

Obviously, these situations are somewhat artificial. Still, when the researchers observed the participants' behavior — and surveyed them afterwards on how strong their urge to bite was — they found something interesting.

"People had a higher urge to engage in the behavior in the stressed condition and the bored condition, much more than in the relaxed condition," Roberts says. Other surveys of nail biters and hair pluckers have come to similar conclusions. "It seems fairly clear that there's some emotional regulation involved."

Why we bite our nails instead of other alternatives

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Of course, this theory still prompts a more basic question: why does biting your nails — or plucking your hairs or picking at your skin — provide pleasure or distraction in the first place? Why do so many people become addicted to these grooming habits, rather than, say, balling their hands up into fists?

One possible answer relates to the finding that people with body-focused repetitive disorders tend to be perfectionists. It might be that ripping off an oddly shaped nail can provide a satisfying sense of perfection for the biter — and the quest for this satisfaction eventually gets out of control.

It's also possible that the uncontrollable urge to groom excessively goes much deeper than we realize. Lots of other animals, after all, seem to do it, too: some cats lick themselves excessively, leading to fur loss, while some horses bite their own flanks over and over. Perhaps the urge to groom past the point of usefulness — to the extent that we actually cause damage to ourselves — is a trait that can be traced way back to the evolutionary ancestors we shared with these other mammals.

Finally, there's a more mundane explanation. Maybe we just bite our nails because they're there. Psychologists believe that you can get psychologically (not chemically) addicted to pretty much anything: any activity that provides a reward can reinforce itself over time.

For an understimulated mind looking for a momentary distraction, the hands are always present. Biting and ripping off a nail can provide a distinct reward (it sounds weird, but to a biter, there's something distinctly satisfying about removing it). Nails grow back, so there's always a fresh one to bite. Do it enough times, and you start to get pleasure from the habit — so whenever you're bored, stressed, or frustrated, your brain unconsciously goes back to it.

How to quit biting your nails

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Different psychologists recommend slightly different techniques for quitting, but they mostly boil down to one common strategy: identifying the circumstances that lead you to bite, and changing them. "We try to identify all the triggers and control them in various ways — either by blocking them or by finding substitutes," Penzel says.

For instance, if you habitually bite your nails while watching TV, you might chew gum or use your hands to play with an object whenever you sit down on the couch to watch. You might also set out signs and reminders next to the couch, reinforcing the idea that you do not want to bite.The same goes for different emotions or feelings that usually make you bite: if being frustrated is a trigger for you, try to alter the circumstances in some way, by giving yourself something else to do or making it harder to bite.

If you still can't stop, there's also a way to make nail biting way less palatable no matter what the circumstance: clear nail polishes that taste absolutely terrible. They're harmless, but once you paint these on, even brief contact between your mouth and your nails will leave a bitter, disgusting taste in your mouth until you eat something else. Some people have success combining this with other strategies.

Regardless of the particular technique you use, a big thing to keep in mind is that breaking your addiction might not come all at once, so if you break down and bite it doesn't mean you have to give up completely. Abstaining for longer and longer chunks of time can still help break down the habit — until, someday, the bizarre habit of nail biting no longer has the same hold on your mind.