There are many reasons for having breast milk, specific analysis is as follows: 1. Pregnancy and lactation, during these two special periods lactogen in the body will increase a lot, stimulating the breast to secrete milk, these two periods have milk is a normal physiological performance. 2. Mastitis, nipple rupture, bacteria into the milk ducts leading to breast inflammation, there will be breast swelling, tingling, nipple swelling, overflow, may flow white liquid, need to carry out If there is pus, puncture or surgery is needed to drain the pus. 3. Breast cancer, cancer patients will have nipple overflow, erosion and pain, and the nature of the overflow is white, yellow and red, which requires high attention, immediate medical examination, pathological examination of tumor benignity and malignancy, and then anti-cancer treatment to prevent more serious sequelae.