In clinical practice, ductal dilatation of the breast 4 mm is more serious. Dilated milk ducts are not a separate disease, but a group of chronic inflammatory lesions of the breast based on dilated milk ducts, with different clinical manifestations and pathological features in different stages. In general, there are many diseases that cause dilation of the breast ducts, including obstructive mastitis, chemical mastitis, acantholytic mastitis, and plasmacytoid mastitis, etc. Usually, these are the causes of dilation of the breast ducts in patients. The early clinical manifestations of the disease are brownish discharge from the nipples or yellowish overflow, or even bloody overflow in some patients, which can involve multiple ducts of the breast. In general, once the breast ducts are dilated, the treatment is still mainly surgical, and the preoperative site of the dilated breast ducts must be precisely located and precisely removed so that the patient can recover healthily.