Boys long hair around the mouth may be a normal physiological phenomenon, may also be due to precocious puberty, taking hormone drugs and other reasons. 1. Normal physiological phenomenon: boys before puberty, the upper lip area will store vellus hair, this time the vellus hair is short, thin, soft, light color, sparse, and slow growth rate; with the boys into puberty, androgen secretion increases, the male second features gradually appear, vellus hair will become black beard. 2. Precocious puberty: If the child’s age is small, the appearance of vellus hairs around the mouth, accompanied by a change in voice tone, testicular enlargement and other symptoms, consider the manifestation of precocious puberty, go to the hospital for serum sex hormone test, in order to clarify the diagnosis. 3. Taking hormone drugs: taking hormone drugs, drugs, may lead to the emergence of thick hair, increased adverse reactions, it is recommended to consult a doctor; in addition to frequent consumption of chicken liver, pig liver and other foods containing high androgen, may also lead to the boy’s body hormone content increases. Boys with long downy hair around the mouth may also be caused by other factors, it is recommended to rule out the normal physiological factors, and then consult a doctor in order to clarify the cause of the disease.