Children old gnawing nails, may be physiological or pathological factors, physiological factors such as personal habits; pathological factors such as iron deficiency, zinc deficiency, etc., can lead to children old gnawing nails. 1. Physiological factors: children in the growth and development of the oral period, in the absence of timely correction is easy to develop the habit of gnawing nails; at the same time, children in boredom, anxiety and other situations, but also through the gnawing of nails to relieve the way. 2. Pathological factors: when the child has a lack of iron, zinc deficiency, there will be symptoms of xenophagia, showing gnawing nails, but generally speaking, only the more serious iron and zinc deficiency will lead to; in addition, the lack of trace elements, such as selenium, etc., there will be gnawing the performance of the nails. Children gnawing nails, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.