Often bite their fingernails, may be caused by the following reasons: 1, may be a kind of OCD performance, OCD there is a category is particularly easy to focus on their own body, such as the appearance of picking hair, picking scalp, pulling hair, and even repeatedly bite the hand, bite the skin of the hand, these are a form of performance. 2, may be too much anxiety, tension, anxiety, tension is easy to accompany the action Increase, especially with small movements. These may be subconscious, such as picking their hands, pinching their corners, blinking frequently or biting their fingernails, etc. 3, may also be caused by bad habits, some people are easy to bite their fingernails since childhood, and even subconsciously will appear this action. At that time not stopped by parents, after growing up there will be such behavior. If you have the above-mentioned performance, you must actively carry out treatment.