Any non-pregnant or non-lactating women and adult males with fluid accumulation in the breast ducts and overflow from the nipple opening spontaneously or by squeezing is called nipple overflow. The causes of nipple overflow are divided into four major categories: physiological, endocrine disease, breast disease, and drug-induced. (1) Physiological overflow is often a small amount of clear or milky white overflow from both nipples, usually after squeezing. Physiological overflow does not require examination and treatment. (2) Endocrine disease It is often a milk-like overflow from multiple ducts of the breast bilaterally. It is usually seen in pituitary tumor, thyroid disease, glioma, pineal tumor, liver disease, kidney disease, etc. Endocrine hormones such as estrogen, prolactin and thyroxine can be measured to understand the systemic endocrine activity. If brain tumor is suspected, cranial CT examination can also be done. (3) Breast disease is often unilateral nipple discharge. It is usually seen in intraductal papilloma, breast trauma, acute mastitis, ductal dilatation, cystic hyperplasia, and plasmacytoid mastitis. Ductoscopy or mammography can be done to understand the ductal lesions. If breast disease is suspected, mammography may be done. (4) Pharmacologic overflow is often bilateral nipple overflow. Most often seen with the use of anti-TB drugs, contraceptives, sleeping pills, estrogen. If drug-related overflow is suspected, stop using the relevant drugs and observe whether the nipple overflow will stop. (5) Cancerous overflow About 5-10% of breast cancers are accompanied by unilateral nipple overflow, which is mostly bloody or plasma blood or watery overflow, and most of them are accompanied by breast lumps. Unilateral nipple discharge with painless small breast lumps is most often seen in early stage intraductal carcinoma. Bilateral nipple discharge breast cancer is rare. It is also worth mentioning that unilateral breast nipple discharge in men, whether it is bloody or plasma, should be considered as breast cancer. Patients with suspected cancerous overflow are examined in three ways: first, mammography or mammography ductography; second, mammography x-ray examination; and third, smear examination of the overflow. The majority of nipple overflow is caused by benign lesions, and only a small percentage is caused by breast cancer. Therefore, it is not necessary to be very nervous when you find nipple overflow, but you should go to a hospital for specialist examination to make a clear diagnosis.