In adult women, when the nipple is sunken under the skin surface of the areola and does not protrude from the plane of the areola, resulting in a small or large localized mouth, it is called nipple indentation. The degree of nipple indentation varies from a receding nipple to a recessed nipple or even an overturned nipple in severe cases. Some people with poorly developed nipples may have indentation, while indentation caused by breast cancer often results in orange peel signs, discomfort, or lumps in the breast. The causes of nipple indentation can be divided into congenital and acquired causes: (1) Poorly developed smooth muscle of the nipple and areola: the nipple has an opening for the milk duct, smooth muscle fibers around the milk duct, and the indented nipple is pulled inward by bundles of muscle fibers around the milk duct and inserted into the dermis of the nipple. The texture of these muscle bundles differs significantly from that of the milk ducts. (2) Inadequate development of the milk ducts themselves: Inadequately developed milk ducts fail to ductalize and behave as striae. (3) Lack of support tissue under the nipple is also a cause of nipple invagination. (4) Heredity: clinical observation: the mother and her mother’s generation, the grandmother has a history of nipple indentation, the next generation may suffer from nipple indentation than normal people. 2, acquired causes: (1) clothing too tight: especially women in the breast development period wear underwear too tight, more likely to lead to nipple depression. (2) Improper use of bras. Too small, too tight, too early use of bras can cause nipple indentation. Nipple indentation is mainly congenital, but it may also be caused by trauma or surgery, breast tumor and fiber hyperplasia after mastitis, and further examination is needed to clearly diagnose whether it is cancer.