The nipple cannot protrude is nipple invagination, there are congenital and acquired causes, respectively: 1, congenital causes, shortening of the breast ducts, nipple smooth muscle dysplasia and tissue fibrosis lead to. 2, acquired, may be acute and chronic inflammation of the breast, such as mastitis, peri-mammary duct inflammation, lumps around the areola, such as breast fibroids, breast cancer, etc. can lead to, teenagers’ Unreasonably tight bras can also lead to nipple invagination, and nipple invagination can lead to breastfeeding difficulties and periareolar inflammation. If adolescents find nipple invagination, they can correct it by pulling and squeezing the nipple, or they can use nipple corrector, and for difficult to repair nipple invagination, they can also correct it surgically. If the lump is caused by a lump, it will be corrected by removing the cause.