Nipple discharge is one of the three most common symptoms of breast disease, with an incidence of about 3-8%. In addition to systemic diseases, pituitary tumors and medications (which can be ruled out by blood tests and medical history), most of them are caused by lesions of the breast itself. The common causes are intraductal papilloma, ductal dilatation, cystic hyperplasia, breast cancer, and acute and chronic inflammation of the breast. The current screening methods for nipple overflow include smear cytology, selective mammography, and ductoscopy. The importance of ductoscopy is increasing because of its high diagnostic rate, visualization of the lesion, and the effectiveness of treatment of inflammation of the milk ducts. The lactoscope was developed in the late 1980s, and in 1991, Ryo Okazaki et al. and Fujikura Co. jointly developed a fiberoptic lactoscope (consisting of a cold light source, an image monitor, an image recorder, and an optical fiber), which is the basis for clinical application. The main clinical applications of fiberoptic lactoscopy are: 1. as an important means of examining the cause of nipple overflow; 2. as one of the best ways to treat lactitis; 3. the simple steps of lactoscopy: 1. dilate the overflowing milk duct (slightly painful); 2. insert the fiberoptic lactoscope and inject liquid containing local anesthetics, antibiotics, and anti-inflammatory drugs (pain disappears); 3. start examining and treating the patient; 4. 4. remove the lactoscope, apply local ointment of aureomycin, and abstain from bathing for 24 hours.