The normal width of the milk ducts is usually within 1mm. Dilatation of the milk ducts by 3.8mm is not serious if it is caused by physiological factors and has no other clinical symptoms. If it is caused by pathologic factors, it is more serious. 1. Physiological factors: due to the effect of hormones during breastfeeding, it will lead to the expansion of breast follicles and ducts. This is generally a normal physiological phenomenon, if there is no discomfort or other symptoms. Generally no treatment is needed. This situation is also not serious. It can be relieved by physical therapy and massage. 2. Pathological factors: 3.8 millimeters of breast duct dilatation has exceeded the normal range value of the breast duct, and the situation is generally more serious. At this time, the expansion may be related to bacterial infection and other conditions. Inflammation caused by bacterial infection leads to the accumulation of inflammatory secretions in the milk ducts, which in turn leads to the blockage of the milk ducts. Due to the blockage of the milk ducts, the constant stimulation of inflammatory substances can lead to dilatation of the milk ducts. Even nipple discharge, high fever, chills and nipple inversion can occur. It is important to treat dilated milk ducts and seek medical attention promptly.