In clinical practice, most of the nipple overflows have no conscious symptoms, and they are seen when their undergarments are contaminated by nipple overflow, and only a few are found during breast examination due to breast pain and lumps. The nature of nipple overflow can be clear water, plasma, plasma blood, blood (fresh or old blood), milk-like, cloudy mucus-like and pus-like when observed by the naked eye. Nipple discharge due to various inflammatory diseases of the milk ducts is often cloudy and purulent. When gently twisting and squeezing the nipple and its root, thickening and hardening of the milk ducts or pressure pain can often be found. Physical examination reveals thickened breast glands, lamellar or nodular and painful. Nipple discharge is not uncommon, but is usually plagioid or cloudy mucus-like and occurs bilaterally. Ductal dilatation of the breast: several ducts may have overflow at the same time, and the overflow is mostly clear water-like, mucus-like or cheese-like, and typical cases can squeeze out viscous fluid like toothpaste when the breast is squeezed hard in the direction of the nipple. In some cases, dilated and thickened ducts are found below the nipple and in the areola area. There may be nipple invagination or dysplasia. When the ductal deposits degrade, they may erode the ducts to form subareolar masses, abscesses, and ductal fistulas, often without nipple discharge due to ductal obstruction, or with cloudy purulent discharge. Intraductal papilloma: The lesions are mostly located in the larger ducts of grades 1 to 3, and nipple discharge is the earliest clinical symptom. The overflow can be plasmacythematous, because the intraductal papilloma is brittle, vascular and bleeds easily; plasmacythematous, old blood or brown overflow is common. Most of the tumors are small and no breast mass can be found, but a few of them may be soft nodules of 0.5~1.0 cm in diameter in the areola area or slightly lateral to the breast, and more fluid may come out from the nipple when pressed. In the early stage of breast cancer, there is often no breast lump or only a small patch of glandular thickening, so it is easy to be ignored. Nipple discharge may be the only clue for early diagnosis and should be paid special attention. Early stage breast cancer or other types of breast cancer invading the ducts may cause nipple discharge of various nature, but clear watery, plasma, plasma blood and blood nipple discharge are the most common. If the nipple discharge is accompanied by an infiltrating mass in the corresponding area of the breast, malignancy is more likely. When nipple discharge occurs clinically, it should be differentiated between systemic or local breast factors. In particular, nipple discharge from a single duct of a single breast should be further examined to identify the cause and site of the lesion. Statistics show that clear watery, plasma, plasma blood and bloody nipple discharge are often associated with precancerous lesions such as breast cancer or intraductal papilloma of the breast, which mostly require surgical treatment. In nearly 50% of hospitalized patients, nipple discharge may be caused by intraductal papilloma or breast cancer, and may be the only symptom of early breast cancer in particular, which should be noticed.