Many people engage in behaviors that range from nail biting, thumb sucking and foot tapping to more physically harmful behaviors like teeth grinding, hair pulling or head banging.
Habit disorders consist of stereotypical repetitive, seemingly driven and non-functional motor habits that often interfere with normal activities and may lead to injury to a body part. The majority of these behaviors are considered harmless and considered part of normal growth and development, but in some cases, the habit persists into adulthood and can be very distressing.
Habits like nail biting are very common and often go unnoticed. However, often the repetitive nail biting can lead to severe injury to the fingers, leading to a variety of infections and deformities. Nail biting is commonly first seen in preschool age up to adolescence and happens in as many as 50-60 percent of individuals. With time, most children grow up out of this habit. However, at least 3-8 percent of the adult population continue to bite their nails. The majority of these people who bite their nails have some degree of anxiety, obsessive compulsive personality or impulse control problem.
Nail biting is slightly more common in females at all ages. While nail biting may be benign, it can lead to extremely short fingernails, infections of the nail, oral herpetic infection, herpetic whitlow, damaged dentition, fracture of teeth and even gum infections. Moreover, the nail and finger often look aesthetically unpleasing.
Like most things in psychiatry, no one really knows why people bite their nails repetitively. Three common reasons include genetics, a poor environment and a difficult childhood.
For most people who bite their nails, treatment is only required if the nail biting is persistent and causes distress to the person. Additionally, if the habit is so severe that it has caused damage to the nails and recurrent infections, then it is wise to seek therapy.
The treatment of nail biting includes some type of behavior therapy that helps reverse the habit. These habit reversal treatments include relaxation, self-monitoring, reinforcement, use of bitter tasting substances on the nails and even wearing dental occlusive splints so that you cannot bite on the nail. However, in many adults who bite nails, behavior therapy alone is not effective and some type of drug therapy may be required. Many adults who practice nail biting also have emotional stress, anxiety or other behavior related problems. In such cases, these disorders also have to be addressed in order to successfully treat nail biting. The drugs of choice are the SSRIs. These medications have a low risk of adverse reactions and they promote compliance. Overall, it appears that with therapy, 60-80 percent of people can be treated but there is a high relapse rate if stress is recurrent.
Source: http://emedicine.medscape.com/article/914071-followup