Some of the patients with breast disease exhibit symptoms of nipple discharge (referred to as, breast overflow), which is a clinical sign, not a disease name. So, what diseases are accompanied by such symptoms? First, the symptoms of breast overflow are only present when the epithelial cells of the breast ducts have a secretory function. Secondly, there are two types of breast overflow. First, physiological overflow, such as during pregnancy and lactation. Secondly, secondary breast overflow, including pathological, partially physiological, and drug-related. The second condition is predominantly seen in patients attending the clinic. We define nipple overflow as milk secretion unrelated to breastfeeding. Regarding the types of breast overflow, there are five general types: 1. plasma; 2. watery; 3. colored milk overflow; 4. milk; 5. bloody. The first three types are mainly caused by hyperplastic lesions, ductal dilatation, cysts, etc. The fourth type is mainly physiological, and some patients belong to endocrine-derived breast overflow. Finally, let’s talk about the fifth type, namely bloody nipple overflow. This type can be caused by conditions such as hyperplastic lesions of the breast, ductal dilatation with chronic inflammation, or it can occur due to tumor lesions, such as intraductal papilloma, carcinoma in situ, invasive ductal carcinoma, etc. The above mentioned is not scary, but the most important thing to remember is: go to a regular hospital to see a breast surgeon if you have symptoms!