Dilatation of the milk ducts by 1.5 mm can be seen in physiological and pathological causes, physiological such as lactation, pathological can be seen in plasma cell mastitis and so on. 1. Physiological factors: mainly seen in the stage of breastfeeding, due to the influence of estrogen, progesterone and other hormones will make the mammary ducts dilated to cope with the needs of breastfeeding, usually no treatment is needed, and may be relieved by itself after the end of the breastfeeding period. 2. Breast Duct Obstruction: It can cause dilatation of the breast ducts, in addition to acute mastitis and other diseases if secondary bacterial infection occurs. 3. Plasma cell mastitis: Ductal dilatation is the main symptom, it is a non-bacterial inflammation, which is mainly manifested as localized discomfort, swelling and pain in the breast. If there is abscess formation, it should be incised and drained in time. Breast cancer and intraductal papilloma may also lead to ductal dilatation, which should be treated promptly.