Moustache growth in girls may be caused by physiological reasons, genetic factors and polycystic ovary syndrome, etc. It is recommended to consult a doctor. 1. Physiological reasons: After puberty, especially in girls, not only the secretion of estrogen is strong, but also the secretion of androgen is very strong, so it will produce androgenic characteristic manifestations, such as growing a moustache. 2. Hereditary factors: If the parents have strong body hair, the children will have more hair because of the genetic problems in their bodies, and the phenomenon of girls growing moustaches will occur. 3. Polycystic Ovary Syndrome: Polycystic Ovary Syndrome (PCOS) is a complex endocrine and metabolic abnormality caused by a common disease in women, suffering from PCOS, the phenomenon of moustache growth may occur. After excluding physiological reasons, women with moustache growth should go to the hospital in time, ask the doctor to clarify the cause of the disease, and actively cooperate with the doctor’s treatment.