Nail biting, also known as onychophagy or onychophagia, is an oral compulsive habit of biting one's fingernails. 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 children bite nails. More pathological forms of nails biting are considered an impulse control disorder in the DSM-IV-R and are classified under obsessive-compulsive and related disorders in the DSM-5. The ICD-10 classifies the practice as "other specified behavioral 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 behavior is not always clear. The earliest reference to nail biting as a symptom of anxiety was in late sixteenth century in France. Signs and symptoms Nail biting usually leads to harmful effects to the fingers, like infections. These consequences are directly derived from the physical damage of biting or from the hands becoming an infection vector. Moreover, it can also have a social impact, for example social withdrawal and avoiding handshakes. The ten fingernails are usually equally bitten to approximately the same degree. Often, the adjacent skin is bitten off, too, which is called perionychophagia, a special case of dermatophagia. Biting nails can lead to broken skin on the cuticle. When cuticles are improperly removed, they are susceptible to microbial and viral infections such as paronychia. Saliva may then redden and infect the skin. In rare cases, fingernails may become severely deformed after years of nail biting due to the destruction of the nail bed. Nail biting may have an association with oral problems, such as gingival injury, and malocclusion of the anterior teeth. It can also transfer pinworms or bacteria buried under the surface of the nail from the anus region to the mouth. If the bitten-off nails are swallowed, stomach problems can occasionally develop. Nail-biting can be a source of guilt and shame feelings in the nail biter, a reduced quality of life, and increased stigmatization in the inner family circles or at a more societal level. Related disorders Other body-focused repetitive behaviors include excoriation disorder (skin picking), dermatophagia (skin biting), and trichotillomania (the urge to pull out hair), and all of them tend to coexist with nail biting. As an oral parafunctional activity, it is also associated with bruxism (tooth clenching