Acute mastitis is a purulent infection of the breast, mostly seen in women who are breastfeeding, and more common in primiparous women. I. Causes: 1. milk stagnation, poor drainage; 2. bacterial invasion, due to nipple breakage or cracking. The patient feels breast pain, local redness, swelling, burning, fever, rapid heartbeat, elevated blood white blood cells, abscesses can be formed. Prevention: 1, to prevent nipple injury, keep the nipple clean, can be washed with warm soapy water; 2, breastfeeding on time, as far as possible to empty the milk; 3, pay attention to the baby’s oral hygiene, to avoid the baby sleep with the nipple; 4, such as milk stagnation, massage or sucking out with a breast pump; 5, nipple broken or cracked to timely treatment; 6, such as nipple invagination, can often squeeze, lift and correct. Treatment: 1. local hot compresses; 2. antibiotics under the guidance of a doctor; 3. if there is an abscess, an incision is needed to drain the pus. Breastfeeding: Stop breastfeeding on the affected side and suck up the milk with a breast pump to avoid stagnation; the opposite side can breastfeed.