Cow’s milk allergy is a common food allergy among infants. Symptoms of cow’s milk allergy are wide-ranging and depend on the mechanism involved. There are immunoglobulin E (IgE)-mediated, non–IgE-mediated, and mixed mechanisms of food allergy. Symptoms of IgE-mediated cow’s milk allergy may be mild or may progress to anaphylaxis, which can be life-threatening. Non–IgE-mediated allergy includes food protein–induced allergic proctocolitis (FPIAP), food protein–induced enterocolitis syndrome, food protein–induced enteropathy, and Heiner syndrome (pulmonary hemosiderosis). These diagnoses comprise about half of all cow’s milk allergies. The most common manifestation of cow’s milk allergy in infants is FPIAP. FPIAP is commonly seen in healthy, full-term infants who present with rectal bleeding and are otherwise well-appearing. This can occur in both formula-fed and exclusively breastfed infants. Food proteins secreted in maternal breast milk can contribute to the development of these symptoms. Maternal cow’s milk elimination diet is often successful in helping resolve symptoms. A period of reintroduction of cow’s milk resulting in re-emergence of symptoms in stable asymptomatic infants is an excellent diagnostic tool to confirm a cow’s milk allergy. Preterm infants are susceptible to food allergy, as demonstrated from several case reports of necrotizing enterocolitis–like illnesses that responded clinically to cow’s milk elimination. Further study is needed about food allergy in the preterm infant population.

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