Nail biting, or onychophagia, is a common habit that is difficult to stop. Nail biting may be related to certain psychiatric disorders, according to a study by Ahmad Ghanizadeh published in the June 2008 issue of the journal, "Child and Adolescent Psychiatry and Mental Health." Nail biting also occurs in those without psychiatric disorders.
Attention-Deficit/Hyperactivity Disorder, or ADHD, was the most common mental disorder associated with nail biting in Ghanizadeh's study. Children and adults with ADHD have difficultly focusing and controlling impulsive behavior. Some sufferers are also physically over-active. Symptoms include daydreaming, easy distraction, fidgeting, trouble paying attention, acting without thinking and excessive talking, the Centers for Disease Control and Prevention, or CDC, says. There are three different types of ADHD. Predominantly inattentive type is characterized by disorganization, distractability and inattention to details. Fidgeting, interrupting and impulsivity characterize predominantly hyperactive-impulsive type. Combined type has equal characteristics of both.
Oppositional Defiant Disorder
Some children suffering from oppositional defiant disorder, or ODD, are nail biters. It may affect as many as 20 percent of school-age children, according to Medline Plus, a website by the National Institutes of Health. It is believed to result from a combination of social, psychological and biological factors. Children with ODD are hostile and disobedient toward authority figures such as teachers and parents. They may get angry frequently and be argumentative, vengeful and easily annoyed. To warrant a diagnosis of ODD, this behavior must persist for at least six months and be severe enough to result in serious problems at school and in other activities.
Primary Motor Stereotypies
Sufferers of primary motor stereotypies, or stereotypic movement disorder, compulsively repeat rhythmic, predictable and "purposeful but purposeless movements," Johns Hopkins Medicine explains. They are normal otherwise. Typical movements include nail biting, hand-flapping, rocking back and forth, head nodding, hair twirling, lip biting and head banging. Excitement, tiredness, stress or boredom usually precede the movements, which usually last a few seconds or minutes. This disorder tends to fade over time, although in some cases it may persist into the college years. The movements are called secondary motor stereotypies if they occur with autism or another neurological disorder.