1.Physiological reasons In 2/3 of non-lactating women, if the nipple is clean, a small amount of fluid can be squeezed out through breast massage or mild pressure suction, and the color can range from white, yellow, green to brown and dark blue. No special treatment is needed for this condition. 2.Bloody nipple discharge during pregnancy Bloody nipple discharge during pregnancy or breastfeeding is mostly caused by excessive blood vessels in the developing breast tissue, and does not need special treatment. Intraductal papilloma is a lesion located in the ducts under the areola, about 50% of them show bloody nipple overflow, which is a benign disease, and can be diagnosed by lactoscopy, and needs surgery. 4. Breast cancer: Most of the breast cancer is characterized by bloody overflow, and a definite breast lump can be detected, which can only be diagnosed through surgery. Periductal mastitis is characterized by purulent nipple discharge, sometimes complicated by nipple inversion, and requires surgery. 6. Ductal dilatation Mostly cheese-like, toothpaste-like mucous nipple discharge, sometimes can be manifested as green discharge from multiple ducts. Pituitary tumor: Bilateral large amount of milk-like overflow which is not related to pregnancy and breastfeeding. The level of prolactin in the blood is obviously increased, and there is often a history of amenorrhea or relative infertility. Pituitary tumor is mostly diagnosed by CT or MRI of the pituitary gland. With appropriate medication or surgical treatment of pituitary tumor resection, the nipple discharge may disappear.