Acute mastitis is an acute purulent infection of the breast. Patients are mostly postpartum breastfeeding women, especially primiparous women, and often occur 3-4 weeks after delivery. To prevent mastitis, it is important to understand the causes of its onset. The main reasons for this are twofold: 1. milk stagnation: milk is the ideal medium, milk stagnation will be conducive to the growth and reproduction of invading bacteria; 2. bacterial invasion: cracked or broken nipples, so that the invasion of bacteria along the lymphatic vessels is the main route of infection. Due to the lack of experience in breastfeeding, at the same time 6m infants have more teething, easy to cause nipple damage, thus occurring mastitis. The key to preventing mastitis is to avoid stagnation of milk, prevent nipple damage, and keep it clean. The actual method: 1. Wash both nipples with warm water and soapy water frequently. 2. If there is invagination, squeeze, lift and correct it frequently. 3, to develop a good habit of regular breastfeeding, the baby does not contain the nipple to sleep. 4.Every time you breastfeed, you should suck up the milk, and if there is any stagnation, you can massage or use a breast pump to drain the milk. The nipples should be washed after breastfeeding. 5, the nipples are broken and cracked to be treated in a timely manner. 6, pay attention to the baby’s oral hygiene.