Unilateral porous nipple discharge, if it belongs to breastfeeding or pregnancy, it is considered to be caused by physiological factors; while not breastfeeding, it is considered to be related to diseases such as dilated mammary ducts and breast cancer. 1. Physiological factors: if in the lactation period or in the pregnancy, found to have unilateral or bilateral nipple overflow and other conditions, and no breast swelling and pain, hard lumps, mostly considered a normal reaction, and pregnancy lactation, progesterone changes related. 2. Breast Duct Expansion: It is a particularly complicated disease, usually related to the obstacle of breast duct drainage, bacterial infection and other factors, some patients are due to abnormal blood hormone levels, mainly manifested as nipple milk overflow, areola lumps. 3. Breast cancer: it is a kind of malignant tumor in the breast, related to endocrine abnormality and genetic factors. It is mainly manifested by unilateral nipple milk overflow, skin abnormality and hard lumps in the breast. Unilateral nipple milk overflow may also be caused by mastitis, breast hyperplasia, intraductal papilloma, etc. It is recommended to consult a doctor as soon as possible and analyze the cause of the disease through breast ultrasound, mammogram, and pathological biopsy before starting treatment.