Adverse reactions to cow’s milk affect approximately 0.1% to 7.5% of children. Infants generally present at 1 week to 3 months of age with protracted vomiting, malabsorption, diarrhea, and dehydration (539). Cow’s milk sensitivity is the most frequent cause of this syndrome, but it also occurs with soy, egg, and wheat.

Reactions to cow’s milk proteins may be classified clinically as quick onset (symptoms develop within 1 hour of food ingestion) or slow onset (symptoms develop after >1 hour from food ingestion). Quick-onset allergic reactions are IgE mediated and do not result in structural gastrointestinal damage (540). Slow-onset reactions may also be IgE mediated, or they may be the result of T-cell–mediated immune reactions. Such reactions may result in a macrophage influx associated with cytokine release and direct damage to gastrointestinal tissues (540).