Nipple discharge refers to the overflow of fluid from the nipple during the non-lactating period of a woman. It is one of the common clinical symptoms of breast disease, second only to breast lumps and breast pain, and can be caused by a variety of reasons. It can be caused by a variety of reasons. Previously, nipple overflow was divided into physiological nipple overflow and pathological nipple overflow. In fact, physiological nipple overflow should specifically refer to a small amount of milk secretion from both breasts even after breastfeeding has stopped, which can last for months or even years, mainly due to stimulation of the breasts by frequent touching and sucking, and therefore no other symptoms such as menstrual cessation and normal serum lactogen tests. It does not require clinical management as long as it is kept clean and no bacterial infection occurs. Pathological nipple discharge can be divided into two categories: systemic causes such as endocrine disorders and lesions of the breast itself. In some women before and after menopause, a small amount of fluid can be discharged from the nipples when squeezed; or in those who have a history of long-term use of contraceptives, recent use of sedatives, rosmarinic acid and other drugs, a small amount of thick, cloudy mucus-like fluid can be discharged from multiple milk ducts in both breasts when squeezing the nipples. Rarely, patients with pituitary prolactinomas often have characteristic non-lactating bilateral breast milk secretion and cessation of menstruation (also known as menopausal lactation syndrome), and larger tumors may present with hemianopia due to compression of the optic nerve and abnormally high prolactin on serologic examination. Bilateral nipple discharge due to systemic causes is mostly secretory nipple discharge, as nipple discharge originates from the secretion of terminal ducts and alveolar cells. This is so that it can be easily distinguished from leaky and exudative nipple discharge due to ductal epithelial cells and their lesions, and most do not require surgical treatment. Epithelial hyperplasia, increased secretion, inflammation, hemorrhage, necrosis and tumors due to ductal or alveolar lesions can lead to nipple overflow, mostly due to unilateral single ductal lesions. Nipple overflow due to disease of the breast itself often requires surgical treatment.