The hair underneath the navel may be related to physiological factors such as heredity, followed by polycystic ovary syndrome, hirsutism and other diseases. 1. Physiological factors: hairy underneath the navel may be related to heredity, androgen level secretion and other factors, is a normal phenomenon. 2. Polycystic ovary syndrome: this disease is closely related to hypothalamic-pituitary dysfunction, ovarian enzyme system function defects, adrenocortical dysfunction, abnormal insulin action, genetic factors and abnormalities in the local regulatory mechanism within the ovary. Mainly manifested as menstrual disorders, hirsutism, obesity, etc., some patients will appear in the navel below the hairy situation. 3. Hirsutism: the etiology is more complex, may and androgen sensitivity increase, gene genetic disease, external stimuli and other factors. It is mostly manifested as local or whole body appears thicker, more and longer hairs than normal gender and age. The cause of hairy under the navel is not one, after excluding physiological factors, it is recommended that patients seek medical examination to clarify the cause of the disease.