Nail biting, also known as onychophagy or onychophagia (or even erroneously onyhophagia), is an oral compulsive habit.  It is sometimes described as a parafunctional activity, the common use of the mouth for an activity other than speaking, eating, or drinking.

Nail biting is very common, especially amongst children. 25-30 percent of kids bite nails. More pathological forms of nails biting are considered an impulse control disorder and are classified under obsessive-compulsive and related disorders.   Nail biting,  the practice as “other specified behavioural and emotional disorders with onset usually occurring in childhood and adolescence,  However, not all nail biting is pathological, and the difference between harmful obsession and normal behaviour is not always clear.