Nipple discharge is a relatively common symptom of the breast, and to understand its origin, we must first talk about its anatomical structure. The breast is made up of glandular lobules, each of which is a dendritic structure consisting of large ducts, branch ducts and glandular vesicles, with the nipple at the center and distributed in a radial pattern. During lactation, the milk secreted by the gland is secreted from the vesicles through the branch ducts and gradually converges to the main duct and then is discharged through the nipple. During the non-lactation period, no fluid should be discharged. Otherwise, it is possible that a disease has arisen, and the more common diseases are, in order: intraductal papilloma, mastopexy, ductal dilatation, inflammation, cancer, etc. Generally speaking, if there is simultaneous overflow from multiple ducts of bilateral nipples, it is most likely to be caused by mastopathy and ductal dilatation. If there is unilateral or single ductal overflow, a closer examination should be done. The method is to use a single index finger to press sequentially around the areola, and when pressure is applied to a point where you suddenly see overflow from a particular duct, remember that orientation, the lesion is mostly in its vicinity. Unilateral or single duct nipple overflow is generally most likely to be caused by intraductal papilloma or ductal dilatation. This disease occurs mostly in the dominant duct and therefore, the lesion is mostly located near the nipple. The only way to treat it is by surgery. In cases where the mass cannot be felt, it must first be located as described above, and after locating the duct that is overflowing, a small amount of melphalan can be injected from the opening to pinpoint the location during surgery. Of course, in a few cases it can also be caused by cancer and mostly by early stage cancer.