Infants always bite the lower lip, may be due to physiological or pathological factors, physiological factors such as personal habits, teething stimulation, etc.; pathological factors such as lipitis, can lead to infants bite the lower lip. 1. Physiological factors: when infants imitate the action of adults biting their lips and form personal habits, they will have such a performance; in addition, infants can also be stimulated by teething, appearing in the mouth and teeth itching and pain, and infants will be relieved by biting their lips. 2. Lipitis: when the infant lacks such as zinc, selenium and other trace elements, or vitamin deficiencies, lipitis, lip biting symptoms will occur, in addition, there can be other abnormal symptoms, such as loss of appetite, poor resistance, developmental delays and so on. Infants always bite the lower lip, there may be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.