A generally harmless nervous habit of biting or chewing the fingernails.

Children's nervous habits, including nail biting, are common. Nail biting is in most cases harmless and is best ignored. The most problematic side effect of nail biting (and other nervous habits such as thumb-sucking and nose-picking) is social ostracism—the child may be teased by her or his peers, and adults observing a nail-biting child may conclude that he or she is insecure or stressed. In addition, the sight of fingernails chewed to the ends of the fingers is unattractive.

About 30% of children ages 7-10 bite their nails. Although the habit may subside during adolescence, researchers at the University of Wisconsin estimated that 20% of college students bite their nails at some time during their college years.

Nervous habits often begin as comfort habits in infancy. When an infant feels anxious, frustrated, hungry, or tired, a...