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Food Allergy 

Adverse reactions to foods are classified as being toxic or nontoxic. Toxic reactions are not related to individual sensitivity but occur in anyone who ingests a sufficient quantity of tainted food. Examples of toxic reactions include reactions to histamine in scombroid fish poisoning or to bacterial toxins in food poisoning. In contrast, nontoxic adverse reactions to food depend on individual susceptibility and are either non­ immune-mediated--i.e., food intolerance (Table 1), or immune-mediated--i.e., food allergy. This article focuses on the clinical manifestations of food allergy.

Allergic Reactions

Allergic reactions to food are either IgE-mediated or non­IgE-mediated (Table 2). The role of IgE-mediated reactions in food allergy is well established. Persons who are genetically predisposed to atopy produce specific IgE antibodies to certain proteins to food. These antibodies bind to mast cells and other cells in body tissues and to basophils circulating in the blood stream. When a food protein is ingested, the IgE recognizes it on the surface of these cells; mediators (e.g., histamine) are released.


The skin is a common target organ for allergic responses to food. Acute urticaria is characterized by pruritic, transient, erythematous raised lesions, sometimes accompanied by localized swelling (angioedema). Food allergy accounts for up to 20 percent of cases

Atopic Dermatitis
Atopic dermatitis usually begins in early infancy and is characterized by a typical distribution (face, scalp and extremities), extreme pruritus and a chronic and relapsing course. This inflammatory skin condition is frequently associated with allergic disorders

Dermatitis Herpetiformis
Dermatitis herpetiformis is a chronic papulovesicular skin disorder.

Gastrointestinal Tract

The gastrointestinal tract is another common target organ for IgE-mediated reactions.

Oral Allergy Syndrome
The oral allergy syndrome is characterized by pruritus and edema of the oral mucosa occurring after the ingestion of certain fresh fruits and vegetables.11 The symptoms rarely progress beyond the mouth. The reaction occurs primarily in patients with allergic disease.

Celiac Disease
A number of immunologic reactions to food proteins are not mediated by IgE. Celiac disease presents over a period of months with steatorrhea, flatulence and weight loss.

Allergic Eosinophilic Gastroenteritis
Although allergic eosinophilic gastroenteritis is an IgE-mediated disease in some patients, about one half of patients do not exhibit specific IgE antibody to foods.

Infantile Proctocolitis
The symptoms of infantile proctocolitis are limited to the lower gastrointestinal tract.

Food Protein­induced Enterocolitis and Enteropathy
Patients with enterocolitis induced by food protein are often diagnosed in infancy.

Respiratory Tract

The upper respiratory tract can be a target of IgE-mediated food allergy. Symptoms may include nasal congestion, rhinorrhea, sneezing and pruritus.

Food-induced asthma is an IgE-mediated illness that may result from the ingestion of a causative food or from the inhalation of vapors released during cooking.

Heiner Syndrome
An example of a non­IgE-mediated adverse pulmonary response to food is Heiner syndrome.


Anaphylaxis refers to a dramatic multiorgan reaction associated with IgE-mediated hypersensitivity. Fatal food-related anaphylaxis appears to be more common in patients with underlying asthma.