Nipple discharge is a symptom of breast disease with high frequency. The causes of discharge can be divided into physiological and pathological, and the common pathological causes are intraductal papilloma, breast cancer, cystic hyperplasia of mammary glands and pituitary tumor. 1. Physiological overflow is mainly a normal lactation phenomenon during pregnancy and breastfeeding, or bilateral nipple overflow after taking oral contraceptive pills recently. 2. Pathological overflow is spontaneous overflow from one or both sides of the nipple in non-pregnancy and breastfeeding, which originates from one or more ducts, and can be intermittent or continuous, with a long course of the disease. (1) Intraductal papilloma, which is more common in people aged 40 to 50, is the main cause of nipple discharge. (2) Breast cancer, which can cause bloody, watery, or purulent overflow from a normal-appearing nipple. Spontaneous unilateral uniportal nipple discharge should be alert to the possibility of breast cancer. (3) Dilatation of breast ducts. The first symptom of some patients with this disease is nipple overflow in the early stage. The color of the overflow is mostly light gray or brown. (4) Cystic hyperplasia of the breast is common in women of childbearing age. In some patients, the nipple discharge is yellowish green, brown or colorless plasma, rarely bloody, and there are no tumor cells in the cytological examination. (5) Pituitary adenoma, due to abnormally high prolactin in the blood, causing nipple discharge, the patient is also accompanied by headache, narrowing of the visual field, etc., and the diagnosis can be confirmed by cranial CT examination. It is recommended that patients go to regular hospitals for examination to distinguish whether it is physiological or pathological nipple overflow, so as to facilitate further treatment in the later stage.