It is not normal for the nipples to be indented, but it can occur in some women and is called nipple invagination. The first is caused by congenital development, which can be divided into true invagination and false invagination. In the former case, the nipple is completely invisible in the areola area and the nipple cannot be turned out by hand pulling. In the case of false invagination, the invaginated nipple can be seen in the areola area of the nipple, and the normal shape of the nipple can be restored or partially restored when the nipple is pulled by hand. The second cause of nipple invagination is secondary to other diseases of the breast, mainly malignant tumors of the breast, such as breast cancer or mastitis during lactation or non-lactation, which can cause soft contraction of the breast tissue below the nipple, thus pulling on the nipple and causing nipple invagination.