Nipple overflow is one of the common symptoms of breast disease. Nipple overflow can be self-inflicted or flow out when squeezed by hand. The nature of this is milk-like, water-like, purulent, plasma or blood-like, etc. The reasons for this are summarized in three types. 1, physiological: in the physiological situation of the breast duct epithelium has a certain physiological activity, can appear a small amount of transparent or milky white nipple overflow. 2, systemic diseases caused by: especially certain endocrine diseases, such as pituitary tumors cause hyperprolactinemia nipple overflow (overflow – amenorrhea syndrome), often bilateral multi-ductal nipple overflow, a few cases of certain drugs can also cause. 3, caused by breast disease: the most common breast diseases that cause nipple overflow are acute inflammation of the breast, ductal dilation, mastopexy, intraductal papilloma, intraductal papillary carcinoma, and breast cancer. Bloody overflow is often unilateral, spontaneous or squeezed out, bright red, light red, light brown or coffee-colored, mostly caused by intraductal papilloma, but also seen in breast cancer. If there is nipple overflow, no matter what kind of overflow and what kind of nature, it should be taken seriously because most of the non-lactating nipple overflow is a manifestation of various breast diseases. Since malignant lesions are more likely to cause bloody overflow, you should be highly alert to any kind of overflow, and male patients should not take the occurrence of nipple overflow lightly and go to the hospital to confirm the diagnosis.