Some swelling on one breast of a breastfeeding mom may be caused by milk stagnation, mastitis and other reasons. It is recommended to go to the hospital in time to find out the cause of the disease. 1. Breast milk stagnation: It is caused by the accumulation of breast milk in the breast which cannot be discharged in time or the baby does not suckle in time. Symptoms such as localized redness, swelling and fever of the breasts may occur. Cold compresses can be applied to reduce swelling, lower the local temperature, eliminate swelling and relieve pain. 2. Mastitis: Generally divided into bacterial mastitis and non-bacterial mastitis, the clinical manifestation of mastitis is the redness, swelling, pain, poor milk drainage, local skin temperature rise and other symptoms. It is recommended to stop breastfeeding, empty the milk with the help of a breast pump, and choose the appropriate antibiotics according to the patient’s condition. During breastfeeding, pay attention to breast hygiene, correct breastfeeding posture, change underwear frequently, keep breast hygiene and clean. Breastfeeding mothers with some swelling in one breast should also consider breast trauma, breast tumor and other factors, it is recommended to go to the hospital in time for examination to exclude other lesions of the breast.