Nipple discharge is called nipple overflow in technical terms. Nipple overflow can be caused by a variety of breast diseases and is also easier for patients to notice. It is one of the main reasons why about 10% of patients come to the clinic, and is second only to breast lumps and breast pain in terms of incidence among the symptoms of various breast diseases. In addition, the nature of nipple overflow varies, and can include milk-like overflow, purulent overflow, yellowish overflow, and bloody overflow. The percentage of patients whose first symptom is nipple discharge is about 5%, and it is mostly found in intraductal carcinoma, papillary carcinoma, etc. The nature of nipple discharge in breast cancer patients can be bloody, plasma or watery, but bloody discharge is more common; however, it is not necessarily breast cancer if bloody discharge occurs. It is also important to note that if the bloody discharge occurs in postmenopausal women or is accompanied by a hard lump next to the areola, you should be alert to the possibility of breast cancer. The characteristics of nipple discharge in different breast diseases Nipple discharge can be classified according to its physical characteristics: bloody, serous, plasma, watery, purulent, and milk-like. Among them, plasma, aqueous and lactic overflows are more common, and bloody overflows account for only 10% of overflows. When the lesion is located in the large duct, the overflow is mostly bloody; when it is located in the smaller duct, it can be light blood or plasma; if the blood stays in the duct for too long, it can be dark brown; when there is inflammation combined with infection in the duct, it can be mixed with pus, liquefied necrotic tissue can be watery, lactic or brown liquid; the fluid of ductal dilatation is often plasma. Most hemorrhagic overflows are caused by benign lesions, but a few breast cancers can also be hemorrhagic. Physiologic nipple discharge is mostly bilateral, and the fluid is often lactic or watery.