Dilatation of the milk ducts with overflow may be related to the obstacle of drainage of the milk ducts, infection, hormonal stimulation and other factors. 1. Dysfunction of mammary ducts: Congenital deformity and inversion of nipple may lead to hyperplasia of mammary duct epithelium, which may lead to narrowing of mammary ducts. Prolonged accumulation of secretions in the milk ducts may cause dilatation of the milk ducts, which may lead to overflow. 2. Infection: When the body’s immunity is low, bacteria and other pathogenic microorganisms invade the nipple, areola and other parts of the body. Bacteria can clean into the skin and subcutaneous involvement of the breast ducts, which in turn leads to the dilation of the milk ducts with overflow. 3. Hormonal stimulation: Increased levels of androgens and prolactin in a woman’s body may stimulate abnormal dilatation of the milk ducts, accompanied by overflow. There may be other clinical causes of ductal dilatation with overflow, it is recommended to go to the breast surgery department of the hospital as soon as possible in order to clarify the cause of the disease.