Food allergies represent a significant problem in the western world, affecting about 7% of children under 3 years of age.^1,2 The impact of food allergies extend beyond the affected individual to their immediate family, as a great deal of anxiety is generated by the fear of a possible fatal food allergy and the practical problem of food avoidance.^3–5 Consequently it is essential that a correct diagnosis be made.

INTERPRETATION OF THE CLINICAL HISTORY

Diagnosing immediate hypersensitivity to food should not be expected to cause difficulty with the onset of well characterised symptoms occurring only minutes after ingestion. The observation that a positive diagnosis of food allergy could be confirmed in less than 50% of cases diagnosed by clinical history illustrates that the true picture is more complex and that diagnostic testing is required to confirm or refute the presence of allergy.^6,7

There are several reasons for getting the diagnosis wrong. Foods are rarely eaten singly, and unravelling the allergen in a meal requires detailed knowledge of food manufacture as well as food recipes. Cooking a food changes the protein structure and this may affect the allergenic properties, so that, for example pasteurised milk becomes less likely to provoke an allergic reaction than unheated milk, but roasted peanuts are more likely to cause symptoms than untreated ones.⁸

Interpretation of allergic symptoms frequently causes difficulty. Eczematous patients, many of whom suffer from food intolerance, experience perioral urticaria and contact irritation provoked by fruit juices and other irritants. Patients with the oral allergy syndrome describe intra-oral pruritus and pharyngeal swelling which is a localised mucosal response without systemic involvement and related to the presence of type I IgE mediated hypersensitivity.^9–11 Patients with ordinary or physical urticaria not infrequently attribute their rash to …