Hair growth on the back of the hand may be caused by physiological reasons, drug factors, polycystic ovary syndrome, Cushing’s syndrome and other factors. 1. Physiological reasons: because the back of the hand has hair follicles, so, there will be hair, the general amount of hair is not much, is a normal physiological phenomenon, no need to worry too much. 2. Drugs: If you use cortisone, streptomycin, phenytoin sodium, testosterone, cyclosporine, etc., you may experience the phenomenon of hair on the back of the hand due to the effect of drugs. 3. Polycystic ovary syndrome: a common reproductive endocrine metabolic diseases, patients can appear irregular menstrual cycle, acne, hair loss, obesity and other phenomena, and can be due to increased levels of androgens, stimulate the growth of hair follicles, the phenomenon of hairy back of the hand. 4. Cushing’s syndrome: patients can be due to the hypothalamus – pituitary – adrenal axis mismatch, resulting in the adrenal cortex secretion of excessive glucocorticoids, resulting in the back of the hand hairy, and will be accompanied by centripetal obesity, muscle atrophy, menstrual disorders or sexual dysfunction and other phenomena. In addition, there are many other causes can cause the back of the hand long hair, it is recommended that timely to the hospital to exclude non-disease factors, follow the doctor’s instructions standardized treatment.