The baby bites the nails for the following two reasons: 1, the lack of trace elements in the body caused by baby nail biting is also called xenophilia, mostly due to nutritional deficiencies, trace elements are essential for the growth of babies, zinc deficiency, iron deficiency are triggering factors, this situation needs to take the baby to the hospital to do trace element testing, the usual diet with balanced nutrition, eat more vitamin-rich fruits and vegetables. 2, psychological factors The nail biting is a common behavioral deviation, mostly psychological factors related to psychological tension and emotional instability, most of the babies with such behavior are more introverted and timid, such as encountering difficult to handle things or being chastised by parents, there will be anxiety. Babies and can not express their mood, will subconsciously through the nail biting to relieve tension, anxiety, again encounter similar situations, the baby will repeat the above behavior, parents do not pay excessive attention to nail biting behavior, to give more baby encouragement, praise, company.