Food allergies are immune-mediated responses to food proteins. Because of differences in the underlying immunologic mechanisms, there are varying clinical presentations of food allergy. This article discusses the manifestations of IgE-mediated disorders, including urticaria and angioedema, rhinoconjunctivitis, asthma, gastrointestinal anaphylaxis, generalized anaphylaxis, food-dependent exercise-induced anaphylaxis, and oral allergy syndrome. It also reviews the presentations of mixed IgE- and cell-mediated disorders, including atopic dermatitis and eosinophilic gastrointestinal disorders. Finally, the manifestations of cell-mediated food allergies are discussed, including dietary protein-induced proctitis and proctocolitis, food protein-induced enterocolitis syndrome, celiac disease, and food-induced pulmonary hemosiderosis.
The clinical presentations of food allergy are diverse. In addition to symptoms of immediate hypersensitivity, there are other more subacute or chronic ways in which food allergy may manifest. In this article, the authors first distinguish food allergy from nonimmunologic adverse food reactions and then discuss the diverse clinical presentations of food allergies as categorized by their underlying immunopathology.
Definition of food allergy and differential diagnosis
Food allergies or hypersensitivities are defined as adverse immune responses to food proteins. It is important to distinguish food allergies from nonimmunologic adverse food reactions, which are considerably more common than true food allergies. Although 20% to 30% of the general population report food allergy in themselves or their children, the prevalence of true food allergy is only 6% to 8% in young children and 3% to 4% in adults. Therefore, many nonimmune adverse food reactions are incorrectly assumed to be allergic.
Examples of nonimmunologic reactions to foods include host-specific metabolic disorders, such as lactose intolerance, galactosemia, and alcohol intolerance. In lactose intolerance, a deficiency in the enzyme lactase results in an inability to digest the carbohydrate lactose found in milk and dairy products. Characteristic symptoms include abdominal pain, bloating, gas, diarrhea, and nausea. Responses to pharmacologically active components or toxins in foods constitute another group of nonimmune adverse food reactions. For example, in scombroid poisoning, histaminic chemicals found in spoiled dark-meat fishes, such as tuna, mackerel, and sardines, result in allergic symptoms on ingestion, including flushing, urticaria, angioedema, nausea, abdominal cramping, and diarrhea. Although the symptoms resemble those of an allergic reaction, the underlying mechanism of scombroid poisoning is nonimmunologic. Another example of a pharmacologically active food component causing an adverse reaction is tyramine, found in aged cheeses and pickled fish, which can trigger migraine headaches because of the aromatic amine content. Finally, psychological disorders, such as anorexia nervosa, food aversions, and food phobias, may also cause nonimmunologic food reactions, as can neurologic disorders, such as auriculotemporal syndrome (facial redness or sweating after eating tart foods) and gustatory rhinitis (rhinorrhea after eating particularly hot or spicy foods). Box 1 summarizes the differential diagnosis of nonimmunologic adverse food reactions.
Host-specific metabolic disorders
Carbohydrate malabsorption
Lactase deficiency (lactose intolerance)
Sucrase-isomaltase deficiency (sucrose intolerance)
Galactosemia
Alcohol intolerance
Response to pharmacologically active food component
Scombroid poisoning (fish: tuna, mackerel, mahi mahi, sardines, anchovies)
Caffeine
Tyramine (aged cheeses, pickled fish)
Theobromine (tea, chocolate)
Toxic reactions (food poisoning)
Fish: ciguatera poisoning (grouper, snapper)
Shellfish: saxitoxin
Fungal toxins: aflatoxins, trichothecenes, ergot
Psychological reactions
Anorexia nervosa
Food aversions
Food phobias
Neurologic reactions
Auriculotemporal syndrome
Gustatory rhinitis
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