Stereotypic movement disorder is more common among boys than girls. The repetitive movements often increase with stress, frustration, and boredom.
The cause of this disorder, when it does not occur with other conditions, is unknown.
Stimulant drugs such as cocaine and amphetamines can cause a severe, short period of stereotypic movement behavior. The behavior may include repetitive and purposeless picking, hand wringing, head tics, or lip-biting. Long-term stimulant use may lead to longer periods of the behavior.
Head injuries may also cause stereotypic movements.