1 Aggression toward themselves
Some theories say people bite their nails due to the fact that they bear inward aggression towards themselves. It may also be a form of self-mutilation.
2 A habit since childhood
Some theories suggest that nail-biting has become a habit since children grow up putting things in their mouths, and sometimes their fingers.
3 Stress, hunger or boredom
Some people bite their nails when they're anxious, stressed, bored or hungry. (See The body language signs of stress)
4 Associated with OCD
In 2012, the American Psychiatric Association linked nail-biting to obsessive compulsive disorder.
5 A sign of perfectionism
A study has found that nail-biters tend to be perfectionists who take out their frustration or stress on their nails.
6 A learned behavior
Nail-biting may sometimes be a formed habit due to being exposed to it in families.
7 An instinctual habit
Some people believe that nail-biting is an instinct passed down to us from our early ancestors. Thus, some people resort to it when they're in need of relief. (See What are the causes of stress?)
8 An escape mechanism
Psychologists have suggested that nail-biting is a way to temporarily escape a bad situation by giving the person a distraction.
9 It feels good
Some people bite their nails merely because they enjoy the feeling of the nail coming off.