I’m sure you know that milk flows from a woman’s nipples during breastfeeding as a normal biological function. Every mother is proud of herself for having the function of breastfeeding. However, some women who are not breastfeeding have toothpaste-like, yellow-green, milk-like, clear water, yellowish, reddish-brown or even blood coming out of their nipples. Under normal circumstances, non-lactating breasts do not have any fluid flowing from the nipples in any case. The medical term for nipple flow is – nipple discharge. Some nipple overflow indicates a certain disease and needs to be treated promptly by the patient. Causes of overflow The female breast consists of lobules, like a small tree lying flat, the leaves are the milk-producing vesicles, the branches are the milk-carrying ducts, and there are 15 to 20 large trunks, or large ducts, opening at the nipple. When breastfeeding, the milk secreted by the glandular vesicles (leaves) travels down the first level of the milk transport ducts (branches) to the large milk ducts (trunks) in the areola, where it is ejected at the opening of the nipple. When there is a malfunction and disease in the ducts that carry milk, such as inflammation in the milk delivery ducts or some small granular tumors growing on the duct walls that often break and bleed, fluid of abnormal color will flow from the nipples. If the sex hormone test is normal, there is no need to deal with it, and it is not recommended to squeeze and knead to prevent damage to the fragile milk ducts. Clear water-like overflow: Clear water-like, often seen in women of childbearing age, with a small amount of clear water flowing from a single or multiple breast ducts, colorless and odorless. A study by a U.S. doctor showed that 50 percent means cancer. It should be actively monitored and checked regularly. Yellowish-green overflow: It is thick and yellowish-green in color. This color is usually associated with a foul odor and sticky consistency, and is often seen as a characteristic manifestation of inflammatory lesions or dilated ducts. Pale yellow overflow: yellow transparent like tea, seen in cystic hyperplasia of the breast, ductal dilatation of the breast, papillomatosis within the breast ducts. Reddish-brown overflow: mostly oxidized bloody fluid, seen in intraductal papilloma of the breast and intraductal papillary carcinoma of the breast. Bloody water-like overflow: red or reddish-brown in color, mostly seen in intraductal papilloma of the breast or breast cancer, but sometimes also seen in ductal dilatation of the breast or breast hyperplasia. Toothpaste-like overflow: It is a characteristic manifestation of ductal dilatation of the breast. Examination methods for overflow Color ultrasound: It is generally difficult to diagnose or see the lesion site by relying on color ultrasound. In rare patients, slightly strong echogenicity can be seen in the dilated breast ducts. Mammography: Mammography is difficult to see microscopic lesions in the ducts and does not allow for a definitive diagnosis. Fiberoptic ductoscopy: It is now possible to clearly enter the duct from the nipple and image the interior of the duct lumen on a computer to understand the lesions within the duct. Overflow smear: Nipple overflow is applied to a glass slide for cytopathological smear examination of the overflow. It can distinguish ductal dilatation, cystic hyperplasia, intraductal papilloma, breast cancer, etc. The principles of nipple overflow disease management Nipple overflow is first distinguished as true overflow and pseudo-overflow. Pseudo-overflow is generally physiological and does not require treatment, or is caused by taking certain medications. After stopping the medication, the symptoms disappear. True overflow requires a series of examinations to find the root cause of the overflow. Based on the nature of the overflow, cytological examination, and what is seen in mammography, we can determine whether the overflow is due to tumor or non-tumor. If the overflow is tumorigenic, it is often due to intraductal papilloma or intraductal papillary carcinoma. In the former case, local segmental resection is performed, while in the latter case, radical mastectomy should be performed. In case of non-tumor overflow, it is often due to ductal dilatation or cystic hyperplasia of the breast. The former can be treated medically or surgically, while the latter can be treated with herbal medicine, medication or surgery.