By nipple discharge, doctors mean the natural overflow of fluid from the nipples except during breastfeeding. Nipple overflow, can be watery, plasma-like (resembling light rice soup), milk-like, bloody, purulent, and many others. Physiological nipple overflow is seen during pregnancy (excluding lactation during breastfeeding). Oral contraceptives and sedative drugs can also cause nipple overflow. Pathological nipple discharge is most commonly caused by intraductal papilloma, followed by ductal dilatation, cystic breast hyperplasia, and breast cancer. Nipple overflow due to breast cancer etc. only accounts for about 5% of nipple overflow and is mostly a dark, bloody overflow. Except for typical physiological nipple overflow (e.g. pregnancy factor), adult women should have their nipples examined by a doctor as soon as they develop nipple overflow. The easiest and most reliable test for nipple discharge is repeated cytologic examination of the discharge smear several times. In addition, a mammogram can show whether the ducts are dilated, stiff, obstructed, disorganized, or have a filling defect. Ultrasound, infrared fluoroscopy, and liquid crystal examination can assist in the differential diagnosis. Patients with nipple overflow, if the doctor thinks it is definitely not caused by physiological or pharmacological factors, should accept the doctor’s advice to have the overflowing ducts removed for treatment, and pathological examination should be performed after removal to avoid missing the diagnosis of early breast cancer.