Ductal dilatation generally refers to the expansion of the mammary ducts, which may be related to factors such as obstruction of mammary duct discharge and abnormal hormonal stimulation. When the proliferation of breast duct epithelium is caused by abnormal nipple development, inverted nipple or congenital defect of nipple, or the narrowing or even occlusion of breast ducts under the stimulation of inflammation and injury, and the continuous accumulation of secretion in the ducts, the dilatation of mammary ducts can be caused. When endocrine disorders occur, the secretion pattern of estrogen and prolactin in women’s blood is disturbed, especially when the prolactin in the blood serum increases excessively, it can stimulate the abnormal secretion of the breast ducts, resulting in the expansion of breast duct hyperplasia. In addition, the dilatation of the milk ducts leads to breast overflow, which also continues to irritate the ducts and may cause secondary bacterial infections in the surrounding tissues. Since this disease is most common in middle-aged non-lactating or menopausal women, it is recommended that regular annual mammograms be performed, and that the nipples and areolas be cleaned and excess secretions removed in a timely manner.