Breastmilk blockage fever may cause hives in infants, and bacteria in the breastmilk may cause infections in infants, further causing hives to develop. Blocked breastmilk often leads to the development of acute mastitis, causing fever in the mother and localized redness, swelling and pain in the breast. The bacteria that cause acute mastitis are mostly Staphylococcus aureus, and when breastfeeding during a severe infection, the bacteria may infect the baby through the milk. Urticaria is a limited edematous reaction caused by a variety of reasons. The main clinical manifestations are windburn and angioedema. Infections caused by bacteria such as Staphylococcus aureus may also cause the development of urticaria. So when an infant develops an infection through breast milk, it is possible to cause the development of urticaria. As the baby’s immune system is not well developed, continuing to breastfeed when the mother has a disease or uses medication may cause the baby to experience corresponding discomfort, so when the mother is not feeling well, she needs to actively seek medical attention and follow the doctor’s instructions for reasonable treatment.