Black hair on the nipple is a normal physiological factor, but may also be caused by dietary factors, polycystic ovary syndrome and other reasons. 1. Physiological factors: there are hair follicles around the nipple, from the developmental period the nipple will start to grow hair, with the growth of age and slowly disappear. 2. Dietary factors: often eat fried, fried and other greasy food, resulting in endocrine imbalance in the body, thus appearing black hair on the nipple. 3. Polycystic Ovary Syndrome (PCOS): a disease caused by endocrine and metabolic abnormalities in the body, characterized by disorders and loss of ovulation and excessive production of androgens in the body. The patient appears to have different degrees of hairiness, upper lip, nipples and around, inner thighs, etc.. Excluding physiological factors, timely consultation should be made to clarify the cause of the disease and appropriate treatment should be carried out if necessary.