Eleven children (median age, 2.6 years; range, 1.8-10.3 years) who had avoided cow's milk for 1.4 to 9.5 years (median, 2.3 years) because of atopic dermatitis underwent double-blind placebo-controlled food challenges. Before the elimination of cow's milk from their diet, all 11 children had had positive skin prick or specific IgE tests, or both, to cow's milk, but had ingested it without the development of acute reactions. After elimination of cow's milk, the dermatitis had not improved, but the diet was continued. During the elimination period, 8 of 11 children developed severe acute allergic reactions after accidental ingestion of cow's milk. During evaluation at the clinic, all 11 children experienced acute allergic reactions to cow's milk (manifesting as urticaria, dyspnea, vomiting, cough, or rhinoconjunctivitis) during double-blind placebo-controlled challenges. The authors concluded there is a considerable chance of developing acute allergic reactions to cow's milk after prolonged cow's milk elimination in children with atopic dermatitis who did not experience acute problems from cow's milk before avoiding it. They suggested that a tolerant state can be maintained by continuous exposure to small amounts of cow's milk.

Comment: Having supervised elimination diets for more than 2,000 patients, I have no doubt that identifying and avoiding allergenic foods is one of the most important components of treating many chronic illnesses. Acute and exaggerated reactions to allergenic foods are common during the first several weeks on an elimination diet, but the severity of the reactions gradually diminishes in most cases with continued avoidance of the offending foods. However, going on an elimination diet will occasionally open up a Pandora's box, in which the patient begins to react to various foods and chemicals to which he or she had not previously reacted. Even if the patient's original symptoms improve, the development of these new reactions can be problematic. The results of the present study indicate that such reactivity to cow's milk can persist for years in some children. In certain cases, it may be advisable to have the patient ingest small amounts of the allergenic food at regular intervals in order to induce tolerance, or to attempt to desensitize the patient to the allergen.

Flinterman AE, et al. Acute allergic reactions in children with AEDS after prolonged cow's milk elimination diets. Allergy. 2006;61:370-374.