Acute mastitis is an acute purulent infection of the breast caused by the invasion and growth of pathogenic bacteria in the breast. It is more common in women who have given birth for the first time and often occurs 3-4 weeks after delivery. The causes of acute mastitis are twofold: on the one hand, the stagnation of milk is likely to lead to the growth of invading bacteria, and the main causes of stagnation are poorly developed nipples (too small or invaginated), which prevent breastfeeding, and excessive milk secretion or low sucking of the baby, incorrect breastfeeding posture, and unclear ducts, which can also cause stagnation; on the other hand, bacteria may also be invaded by broken or cracked nipples. The main way of infection is along the lymphatic vessels. If the baby sleeps with the nipple in his mouth or if the baby suffers from stomatitis, the bacteria can directly invade the milk ducts and travel up to the lobules of the gland to cause infection. Acute mastitis is more prevalent in the first month after childbirth; after 6 months when the baby starts teething, the nipple is also vulnerable to damage and should be carefully prevented; and during the weaning period, you should be alert to the occurrence of acute mastitis. If you have acute mastitis, you will initially feel pain in your breasts, with localized hard lumps and swelling; as your condition progresses, you may also experience coldness, chills or an increase in body temperature, sometimes to 39 degrees or more. Usually, only one side of the breast shows symptoms of inflammation. The affected breast is too painful to press, and the local skin is hot, red and swollen, with hard lumps. And the lymph nodes in the armpit on the same side are swollen and painful when pressed. If you go to the hospital for blood tests, it will show a significantly higher number of white blood cells.