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Why Biting Your Nails and Picking Scabs Feels Weirdly Satisfying

These behaviors are all natural—to an extent.
illustration of woman biting her nails
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"It's just so satisfying."

This is how people often describe their compulsive self-grooming. Like popping pimples. Who doesn't think that's weirdly gratifying? Other examples include nail biting, aggressive flossing, hair plucking (trichotillomania), skin picking, and preventing wounds from healing. We're corporeal creatures, so such activities are natural—to an extent.

But compulsively engaging in these behaviors is, according to modern psychology, pathological. Excessive self-grooming falls under the broad classification of "self-harm": damaging oneself irrespective of intention. And while non-suicidal self-injurious behavior (SIB) isn't technically a disorder—modern psychology's most recent diagnostic manual, the DSM-5, maintains that non-suicidal self-injury warrants further research—psychologists warn that people with SIB need help.


People with a history of SIB are more likely to report interpersonal problems, loneliness, and low quality of life. In animals, self-injurious behaviors ranging from penis self-mutilation in lab mice to obsessive feather plucking in birds are a well-established measure of psychological distress.

Moreover, SIB is highly co-morbid with other disorders. For example, hair pulling is significantly more common among patients with other conditions, like OCD, skin picking, body dysmorphic disorder, and tics. SIB appears in 80 percent of people suffering from mood, anxiety, and substance abuse disorders. Compare that to just 17 percent of the general population (though there's some indication that SIB is on the rise).

If SIB is not normal and not helpful—excessive grooming can result in tissue damage and permanent hair loss, for example—why do people do it? The short answer: It feels good.

For one, SIB can avert boredom. When animals are caged, isolated, or living in un-stimulating environments, self-injurious behavior is much more common. Here's one example: Wild birds are constantly active, interacting with others, searching for food, and nesting. Captive birds live alone for a lifetime with food provided and nothing to do—but pluck their feathers out. Likewise, humans are more likely to hurt themselves when they're unemployed or feeling depressed or powerless. For some, the modern workplace may function as a form of captivity; SIB serves as an escape.


SIB can also help people cope with unpleasant feelings. In captive animals, stressful events—like new surroundings, social stress, routine changes, overcrowding, social isolation, and separation anxiety—often trigger SIB. In one study on house cats, a stressful experience preceded excessive grooming in a full 86 percent of them. We see this effect in the lab, too: Mammals mutilate themselves more often after they've been administered drugs that increase sympathetic activity, which is the fight-or-flight response.

In humans, stressors like PTSD, depression, abuse, and everyday events can incite self-harm. In one study, participants reported that interpersonal difficulties or negative emotions often preceded their SIB. Individuals who pluck their hair, for instance, report that pulling worsens when their anxiety worsens. The prevalence of such behaviors "appears to wax and wane according to prevailing environmental pressures," explains Dan Stein, a psychiatry professor at the University of Cape Town.

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Though it's counterintuitive, SIB can actually have a temporary calming affect. Hair pulling, according to one study, can briefly alleviate stress, boredom and negative emotions. It "seems to regulate unpleasant or aversive feelings," summed another study. In lab monkeys, research suggests that such behaviors may "reduce arousal"—not just emotionally but also physically. Monkeys who bit themselves quickly lowered escalating heart rates. In short, SIB may be a maladaptive form of self-soothing.


But, while SIB may temporarily relieve tension or anxiety, the behavior returns when stress reoccurs, or even in response to the behavior itself. For example, people with bald spots from trichotillomania or scarring from skin picking often feel anxious about going out in public, which in turn exacerbates their condition. As a result, adults with SIB have less day-to-day contact with peers and family members than control groups do. This is how even occasional self-harm can spiral out of control.

Finally, SIB may feel good because it actually, physically feels good. In fact, feelings of pleasure, gratification, or relief when pulling out hair is required for an official diagnosis of trichotillomania. It's not totally clear why pain sometimes equals pleasure, but scientists have found synaptic connections between the brain's pain centers and pleasure centers. When pain centers are stimulated, endorphins are released. Additionally, a particular hormone—"ACTH"—has been linked to compulsive grooming in animals. Some researchers theorize that the way ACTH interacts with feel-good hormones like oxytocin and dopamine may help explain SIB.

Because SIB feels good, it's hard to treat. It distracts people, helps them cope, and even induces physical pleasure, thereby reinforcing the behaviors. The more people do it, the better they feel momentarily, and the more they want to do it—particularly when stressed. Moreover, anxiety impairs impulse control. The more anxious people are, the less willpower they have to resist SIB.


The reinforcement problem is compounded by shame: People with SIB are less likely to seek support for their condition than those with other conditions. Sufferers often fail to tell their doctor about their condition. And because physicians typically only screen for mainstream mental disorders, they often miss SIB.

Sadly, even once SIB is unearthed, treatment is difficult. Though antidepressants like SSRIs are the go-to remedy, they haven't proven superior to placebos for hair pulling or skin picking. When they do work, relapsing is common. In birds, cats, dogs, humans and chimps, antidepressants temporarily relieved SIB symptoms, but subjects were prone to relapses once off the drug or after stressful events. Likewise, behavioral therapy shows a reduction of symptoms immediately following treatment, but relapse rates are high.

But there's some hope. In a study published last month, participants with trichotillomania were more likely to pull their hair if they reported feeling intolerant to thoughts and urges related to hair pulling. Conversely, subjects were less likely to pull if they tolerated such thoughts and urges. In other words, openness and tolerance toward their condition made them less likely to give in to it.

Because people feel embarrassed about their condition, they often shut down self-inquiry and resist support. Successful treatment may be just the opposite. For captive animals suffering from SIB, more effective than any drug is transferring the subject to "compatible social housing." At the end of the day, they need to feel that they're not alone.

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