Nail biting

Casual biting of the nails is a common activity among children, usually after they reach the age of three or four. An otherwise happy child, finding herself bored, a little worried or excited, perhaps by a television program, may bite her fingernails. Nagging about the practice never helps, but instead focuses attention on, and probably prolongs, an activity that otherwise might quickly pass.
Nail baiting that continues for an extended period is usually seen only in children five or older, and often as a response to a specific worry. Try to identify what may be specially troubling your child, and help her deal with it. Think of new activities that involve use of the hands. Encourage pride in the appearance of the hands by emphasizing good grooming, even allowing her to use clear nail polish.
If the nail biting persists and becomes compulsive if your child gnaws constantly at her nails and keeps them bitten to the quick you should get medical advice.