Breast dilation refers to the dilatation of the milk ducts in the breast, mostly caused by physiological, inflammatory, and intraductal tumors. Some women are prone to ductal dilatation during breastfeeding because the breast needs to secrete milk during breastfeeding, so it is prone to physiological dilatation, which generally does not require treatment without local pain or inflammatory manifestations. Inflammation in the breast ducts can also cause ductal dilatation. Inflammation can lead to secretion in the ducts, and the ducts are prone to redness, swelling, heat, pain, and varying degrees of dilatation. Pathological dilation includes breast hyperplasia and tumors in the ducts, which secrete fluid and cause dilation of the ducts, and squeezing of the nipples may be accompanied by nipple overflow. Long-term use of antidepressants and medications for gastrointestinal disorders can also cause dilation of the ducts.