Up to 45% of the population report adverse reactions to food (445). The incidence appears to be increasing, although this may reflect increased patient and physician reporting of allergic symptoms (446). Food sensitivity occurs particularly commonly in infants and young children. Definitive diagnosis of a food allergy requires the demonstration of an unequivocal clinical reaction after a controlled food challenge and elimination of the symptom complex subsequent to removal of the offending food.

The increased susceptibility of young infants to food allergic reactions results from their general immunologic immaturity and the overall immaturity of their gastrointestinal tracts (447,448). The majority of allergic reactions to food are IgE-mediated, mast cell–dependent, immediate hypersensitivity-type reactions. The interaction of an antigen with an antibody or immunocyte triggers the allergic reaction. It is mediated by soluble factors from activated neutrophils, mast cells, and macrophages, or by direct membrane interactions between immune cells and antigens on their cell surfaces. Cytokine and inflammatory mediators are released that act directly on the epithelium, endothelium, or muscle, or indirectly through nerves and mesenchymal cells. The immediate consequences of these mediators include a local change in vascular permeability, stimulation of mucus production, increased muscle contraction, stimulation of pain fibers, recruitment of inflammatory cells, edema of mucosal epithelial villi, increased protein loss from the gut, and increased absorption of foreign antigens. Also, as a result, eosinophils, lymphocytes, and monocytes are attracted to the reaction site, where they release additional inflammatory mediators and cytokines. Repeated ingestion of an allergen stimulates mononuclear cells to secrete histamine-releasing factors, some of which interact with IgE molecules bound to basophils and mast cell surfaces (449). If significant mast cell degranulation occurs, mast cell mediators may provoke potentially fatal systemic anaphylaxis.

A common form of allergic colitis is cow’s milk and soy formula intolerance (450). It may also develop in breastfed infants, probably as the result of transfer of potentially immunogenic substances (especially cow-milk–derived β-lactoglobulin) from the maternal diet into the breast milk (451). Food allergy, whether IgE or non-IgE mediated, affects males and females equally and at any age, but occurs more often in infants and young children with a prevalence of 0.5% to 3%. Allergic proctitis commonly affects young infants who present with rectal bleeding, with or without associated diarrhea (452). Common symptoms include vomiting, pain, weight loss, an allergic history, anemia, and peripheral eosinophilia. Patients may also present with constipation (453).