A mother brought her two-year-old child to the office for examination of a rash that had appeared rapidly on the child's face (see the accompanying figure). The rash was itching intensely and getting progressively worse. Early that morning, the child had eaten a banana, a slice of wheat bread, minced lamb and one boiled egg white. He played actively through the morning and napped for two hours. At 2 p.m., he ate a fresh apple, lettuce and part of a slice of roast beef. Ten minutes later, the mother noticed the rash. The child had no vomiting, abdominal pain, blood in the stool or respiratory symptoms. He did have a history of atopic dermatitis and of urticarial reactions to milk, yogurt, catfish and bananas. He had developed a tolerance to bananas over the past year. The family history was positive for allergic rhinitis. On examination, the erythematous maculopapular rash was found to be poorly defined, involving the lower half of the face but not the lips, tongue, palate or throat. His lungs were clear. The child responded well to topical corticosteroids and oral antihistamine therapy. Within 30 minutes, only traces of the rash were visible.
The answer is C: roast beef. Preserved foods are a frequent cause of food hypersensitivity. The fact that the child ate only a portion of the slice of the roast beef is a clue that he was already starting to feel the intense pruritus typical of a classic allergic reaction. The patient had an immediate hypersensitivity reaction that usually occurs within two hours of contact with the food antigen and consists of pruritus, erythema and edema. If left untreated, the pruritus can reoccur after six to eight hours.1
The foods that were eaten in the morning were less likely to have been the provoking agents because of the time factor. A late-phase reaction does not occur without a preceding immediate hypersensitivity reaction.1 Note that the child by history had developed a tolerance to his banana allergy.
The roast beef in this case contained sodium benzoate, flavorings and food coloring, all of which are known to cause allergic symptoms. Other frequently implicated food dyes, flavorings and preservatives that can cause allergic reactions include tartrazine (FD&C yellow dye no. 5), nitrites and nitrates, monosodium glutamate and sulfiting agents.2
Various fruits and raw vegetables are known to cause oral allergy syndrome. In this symptom complex, the patient first develops pruritus and edema of the lips, tongue, palate and throat. Since the patient in this case did not develop these symptoms, the apple was less likely to be the offending agent.3
IgE-mediated food allergy has been shown to be involved in approximately 60 percent of cutaneous flares in patients with severe atopic reactions.3 In patients with atopic dermatitis, a single contact with a food allergen may not result in cutaneous symptoms.3 Repeated exposure, however, may lead to chronic inflammation and eczematous eruptions.3 Elimination diets that exclude cow's milk, eggs and tomatoes have been shown to reduce severity of symptoms in 75 percent of subjects.1
Children younger than two years with a history of a mild hypersensitivity reaction can be rechallenged up to every four months under close observation.3 On the other hand, patients with allergies to peanuts, fish and tree nuts often do not develop a tolerance to these foods and should not be routinely rechallenged.3
In children, the most common positive food challenges occur with ingestion of egg, peanuts, milk, wheat, soy and fish, in order of frequency. In some cases, cooked foods may be less allergenic than raw foods. In patients over nine months of age, rice, carrots, squash and lamb are less allergenic. In patients over two years of age, fresh lettuce, potato, safflower oil, tea and sugar are also less allergenic. Such foods are initial options for elimination diets.3