Nipple overflow is also known as abnormal nipple secretion in clinical practice, including physiological and pathological. Physiological overflow is common during pregnancy and lactation, and after miscarriage, and is mostly bilateral multi-ductal overflow in both breasts; in addition, some endocrine diseases, during the use of contraceptives and sedative drugs can also occur, and this type of overflow does not require surgical treatment. Pathologic nipple overflow, mostly occurs in unilateral single ducts, and bilateral ducts are rare. The nature of nipple overflow can be of various forms: clear, clear fluid, yellowish, yellow-purulent, pink, bright red, etc. Generally, bloody overflow from a single breast duct often suggests that the lesion is pathologic, and its causes may be: intraductal papilloma, cystic hyperplasia and structural dysplasia of the breast, mammary adenopathy, ductal dilatation, and breast cancer. Therefore, when nipple overflow occurs clinically, especially in a single nipple, it must be noticed, examined and treated promptly.