The shape of the nipple: the female breast is hemispherical or teardrop-shaped, consisting of the skin of the breast, the mammary glands and the nipple and areola. The areola is 3.5-4.5cm in diameter, generally tan in color, and the nipple is generally 0.8-1.2cm in diameter and 0.4-0.6cm in height, with 15-20 milk duct openings on both sides of the nipple, which is the site where women excrete milk. Classification of nipple invagination: Type I: mildly depressed, nipple neck exists, can easily squeeze out the invaginated nipple by hand; Type II: nipple is completely depressed in the areola, can squeeze out the nipple by hand, but the nipple is smaller than normal, mostly without nipple neck; Type III: cannot make the depressed nipple squeeze out. Three types of pictures The case of type I can be improved by massage and breast pump during pregnancy, delivery and breastfeeding, but the case of type II and III need nipple correction surgery for the recovery of breastfeeding function and inflammation prevention. Nipple invagination hazards: 1, nipple depression is detrimental to the beauty of the female form. 2, nipple deep in the areola skin, secretions and pollutants are not removed, easily cause nipple areola inflammation, and even bleeding, erosion, the formation of chronic inflammation. 3, maternal breast milk discharge is not smooth, milk stagnation, prone to acute mastitis, breast abscess. 4, the nipple can not be exposed, the mother can not breastfeed.