Some newborns may develop allergies after breastfeeding, which may manifest as the following symptoms. The first symptom is frequent diarrhea. If the allergy to the proteins in breast milk causes digestive and absorption disorders, causing allergic symptoms in the intestine, which can lead to diarrhea. The symptoms of diarrhea are longer, without fever, and are different from bacterial enteritis, which causes excessive stools. Secondly, the symptoms of vomiting will appear, and frequent vomiting will occur after allergy to breast milk, which is also a very common symptom. Finally, newborns allergic to breast milk can also manifest as eczema of the skin, which is a systemic reaction caused by allergy to the proteins in breast milk, and the eczema of newborns will be repeated, and the symptoms will be relieved after stopping the use of breast milk.