Untreated milk and ordinary formula milk contain more than 32 kinds of proteins with high antigenicity, among which casein and β-lactoglobulin have the strongest immunogenicity. Under normal circumstances, the immune system has tolerance to the above food proteins, but the immature development of intestinal mucosal barrier and immune system in infants and young children leads to allergy to milk protein. The manifestations of human allergy to cow’s milk proteins can be classified into three kinds: 1. IgE-mediated: the main manifestations are acute episodes, with urticaria, angioneurotic edema, rhinitis, asthma, nausea, vomiting, and diarrhea as the main manifestations; 2. Non-IgE-mediated: the main manifestations are delayed or chronic episodes, with colitis and proctitis of the small bowel as the main manifestations; 3. Mixed IgE- and non-IgE-mediated: the main manifestations are delayed and chronic onset, with atopic dermatitis and eosinophilic gastroenteropathy as the main manifestations.