There are three main cases of 20-year-old women without nipples: First, during the adolescent development period, due to wearing inappropriate underwear, resulting in long-term nipple pressure, nipple invagination, should be replaced with loose, breathable, cotton underwear, while hand pulling the nipple, to strengthen the elasticity of the nipple support structure, more can make the nipple back to normal form. Second, congenital factors, mostly refers to the nipple dysplasia, mainly caused by the congenital lack of nipple support, the need for surgical treatment, the surgical method is mainly nipple plasty. Third, pathological factors, refers to the irreversible pathological process of nipple invagination due to some disease in the breast, including breast cancer, breast tuberculosis or intraductal papilloma, etc. Clinical manifestations, in addition to nipple invagination, can also appear breast lumps or nipple bleeding and other symptoms. If you do not have nipples at the age of 20, after excluding physiological factors, you should go to a regular hospital for breast surgery or plastic surgery in a timely manner, avoid wearing too tight underwear in daily life, and moderately give breast massage to promote nipple development.