Nail biting in children is related to psychological factors, xenophagia, and inattention. 1. Psychological factors: 3~4 months old babies have the physiological need to suck, often in hunger and before going to bed sucking fingers, 1~2 years old will gradually disappear. Sometimes small children can not be satisfied psychologically, do not get enough love from parents, lack of companionship, inner loneliness when sucking the thumb, which becomes a habit, and will bite nails when they grow up. 2. Ectophagy: It refers to the persistent addiction of the child to non-edible objects, such as dirt, hair, nails, etc., which is difficult to control by oneself. It may be due to the lack of trace elements in the body, such as zinc and iron deficiency, and may be accompanied by growth retardation, anorexia, low immunity and other symptoms, and may be combined with psychological disorders. 3. Lack of concentration: When children are listening to lectures in class, they can’t concentrate fully and may make various small movements, including biting nails and playing with pens. Children biting nails may have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.