Cow’s milk protein allergy (CMPA) is an immune reaction to proteins found in cow’s milk. It is common in infants. The incidence of CMPA during first year of life is estimated to be 2% to 7.5%. It is the most common food allergy in children younger than 3 years. Milk proteins can either be directly ingested by drinking cow’s milk–based formula or passed through breast milk. CMPA in exclusively breast-fed babies has lesser incidence ( compared to formula fed babies) is thought to be due to β-lactoglobulin of cow’s milk that is found in human milk and usually presents 4 to 6 hours after maternal consumption of cow’s milk
CMPA can be immunoglobulin E (IgE) mediated or non–IgE mediated. IgE is typically immediate, type 1 hypersensitivity (minutes to 2 hours after consumption of cow’s milk) while non IgE-mediated CMPA is delayed, type 4 hypersensitivity.
CMPA usually presents within the first month of life. Most common symptoms are skin symptoms followed by gastrointestinal and then respiratory symptoms. Typically, stool is foamy, with mucus, and non–foul smelling, but it can commonly be blood tinged otherwise normal appearing newborn stool. In exclusively breast-fed infants, CMPA usually presents with atopic dermatitis and/or allergic proctocolitis
Atopic dermatitis is a risk factor for IgE-mediated common food allergies and the suspicion for CMPA should be stronger in moderate to severe atopic dermatitis that starts in the first 6 months of life.