White-collar women and mothers who gave birth by cesarean section are often faced with the dilemma of no or little breast milk after delivery. When faced with a nursing baby, the family’s first thought is to use milk, which may lead to milk protein allergy and feeding intolerance, laying the fuse for the baby to develop allergic diseases later. In recent decades, the incidence of allergic diseases has been increasing worldwide, with high treatment costs, impact on quality of life, and a lack of effective curative measures. Therefore, early allergy prevention is particularly important, and nutritional intervention for newborn babies becomes the most important preventive measure. 1. What do we know about milk protein allergy? In general, the various clinical manifestations of allergic diseases are presented gradually in a chronological order called the allergy course, which means that the manifestations of allergic diseases change in stages as a person ages, with different allergic symptoms appearing continuously in various systems. Untreated regular formula contains more than 32 proteins with high antigenicity and the immune system is generally tolerant to these food proteins. For those babies with immature immune systems and inadequate intestinal barrier function, coupled with the presence of an atopic genetic background in some babies themselves, milk allergy is highly likely to occur. The first dose of milk can be without any discomfort and clinical symptoms, which is clinically called the sensitization phase. After a period of time, milk proteins can be recognized by the sensitized immune cells, and when exposed to the same food or food containing cross-antigens again, a series of specific immune reactions will be triggered, causing characteristic clinical symptoms. The clinical manifestations of milk protein allergy are mainly in the gastrointestinal tract, skin, and respiratory system, with mild-moderate and severe degrees. The earliest symptoms are gastrointestinal: frequent reflux, vomiting, diarrhea, blood in the stool, constipation (with or without perianal rash), iron deficiency anemia. Skin problems: atopic dermatitis, such as eczema, itching, rash, hives, edema, dryness, etc. Respiratory tract after atopic dermatitis has healed: chronic cough, wheezing, allergic rhinitis or asthma. Systemic: persistent discomfort or abdominal pain, crying, irritability. Breast milk is hypoallergenic, homogeneous protein that is not perceived as a heterogeneous protein by the infant’s immune system. It contains secretory IgA, which binds to food antigens and attaches to the surface of the intestinal mucosa, preventing the passage of large molecule antigens through the intestinal mucosa. Breast milk helps to induce oral immune tolerance, and foreign substances in the mother’s diet retain a moderate degree of immunogenicity, giving a mild stimulus to the baby’s immune system. However, some exclusively breastfed babies still show symptoms of allergy, such as recurrent vomiting, persistent diarrhea, constipation or blood in the stool, because allergy can also occur in breastfed babies. The possible reasons for this are: First, the mother’s “intrauterine sensitization” caused by eating a lot of eggs, milk or shelled seafood during pregnancy. The second is that the mother ingested a lot of milk, eggs, shelled seafood and other food proteins during breastfeeding, and these food allergens are passed to the baby through breast milk, resulting in the baby’s allergy. 2. What can we do about milk protein allergy? In order to reduce the allergenicity of milk protein, scientists use enzymatic hydrolysis, ultra-high temperature, ultra-filtration and other technologies to interrupt the conformational antigenic determinants and sequential antigenic determinants of milk protein, and change the peptides with molecular weights between 20,000-1 million daltons contained in ordinary milk formula powder into hydrolyzed protein formula powder with short chain peptides with molecular weights between 160-2,000 daltons, as well as free amino acids, so that the allergenicity of milk The allergenic power of milk is reduced. There are three types of special formula powders for milk protein allergy: (1) Moderate (partial) hydrolyzed protein formula powder: enzymatic hydrolysis cuts off milk protein polypeptides into small peptide fragments, which retain some antigenicity. The baby’s continuous intake of small amounts of milk protein antigen can induce oral immune tolerance and prevent allergies. (2) Complete (deep) hydrolyzed protein formula powder: the end products are mostly dipeptides, tripeptides and a small amount of free amino acids, almost antigen-free, no active immune response, and treatment of allergy. (3) Free amino acid formula powder: also known as allergy-free formula, 100% free amino acids, no food protein. It is suitable for children with severe protein allergy and those who continue to have allergic symptoms despite the application of deeply hydrolyzed protein formula powder. If the baby is exclusively breastfed and still shows symptoms of allergy, then consider replacing breastfeeding completely with free amino acid formula powder for 2-4 weeks or mixing free amino acid formula powder with breast milk. At the same time, breastfeeding mothers should avoid food proteins that may cause allergies, such as milk, eggs, soy, nuts, wheat, fish, shellfish, and chanterelles. During dietary avoidance, mothers should take calcium supplements (1000 mg/d). Dietary avoidance should be continued for at least 2 weeks, or 4 weeks in case of atopic dermatitis or allergic colitis. If dietary avoidance does not improve the child’s clinical symptoms, the mother should return to a normal diet and be seen by a specialist depending on the type and severity of the child’s clinical symptoms. If the child’s clinical symptoms completely improve or disappear during the period of dietary avoidance, the mother can resume one of the avoided foods every week. 3. Nutritional strategies for early prevention of allergy in infants and young children The first milk of a newborn baby’s life should be breast milk. We should pay attention to food allergies in babies and take active measures once they occur to reduce the risk of other allergic diseases in the future. Due to the age-specific nature of the occurrence of allergic diseases, most interventions are concentrated in early childhood, especially in the neonatal period. Recommendations for allergy prevention in babies with evidence-based medical evidence of effective and safe interventions are: exclusive breastfeeding for at least 6 months; if breastfeeding is not possible or breast milk is insufficient, moderately hydrolyzed formula is recommended from birth to at least 6 months; and the introduction of solid foods after 6 months of age.