Girls may have hairy armpits due to heredity, endocrinology, side effects of medication and so on. 1. Heredity: If there is a condition of vigorous body hair in the parents or family, the girl may have vigorous armpit hair. 2. Endocrine: if the girl’s androgen level is relatively high, or there are ovarian cysts, polycystic ovaries and other diseases that lead to high levels of androgen in the body, then there will be the case of exuberant armpit hair. 3. medication side effects: external use of hair growth drugs or long-term use of glucocorticoids and other large quantities, may lead to the situation of the girl’s armpit hair exuberant. There are many reasons for girls to have hairy armpits, if you exclude physiological factors, you can go to the hospital to get a clear picture of the cause of the disease and treat the symptoms.