Milk deposition is beneficial to the growth and reproduction of invasive bacteria. The reasons are as follows: ① nipple is too small or invaginated, which hinders breastfeeding, and pregnant women fail to correct nipple invagination in time before delivery, making it difficult for babies to suck milk; ② Too much milk, incomplete emptying, and the parturient did not empty the excess milk in the breast in time. ③ The mammary duct is blocked due to obstruction, inflammation of the mammary duct itself, tumor and external pressure, and fiber falling off the bra.

2, the invasion of bacteria

It is difficult for infants to suck milk when nipples are inverted, which is easy to cause damage around nipples, and it is the main way for bacteria to invade along lymphatic vessels and cause infection. In addition, the baby often sleeps with the nipple, which will also make the inflammation in the baby's mouth directly invade and spread to the mammary duct, and then spread to the interstitial breast to cause suppurative infection. Staphylococcus aureus is a common pathogen.