Infants biting their lower lips may be related to insecurity, or it may be caused by micronutrient deficiencies, eruption of milk teeth and other reasons. 1. Lack of security: If the child lacks father’s or mother’s love, especially left-behind children, due to the long-term lack of parental companionship, resulting in a sense of insecurity, the phenomenon of biting the lower lip may occur. 2. Lack of trace elements: Some infants lack trace elements due to insufficient dietary intake for a long period of time, especially zinc, iron and other trace elements, which may lead to infants biting their lower lips, and they may also suffer from xenophagia, such as eating mud, dirt, paint and so on. 3. Emergence of milk teeth: When the baby’s milk teeth erupt, due to dental stimulation, resulting in pain and discomfort in the gums, may appear to bite the lower lip, may also be accompanied by the symptoms of drooling. Infants biting the lower lip, may also be related to other factors, parents are advised to find the causes, take the baby to the hospital as soon as possible to avoid delays in the condition.