Food Allergy

A food allergy, or hypersensitivity, is an exaggerate immunological response to a food that can cause symptoms from tingling lips to difficulty breathing and life-threatening anaphylaxis.

The prevalence of food allergies has been estimated to be around 1 to 3 percent in adults and 4 to 6 percent in children and rising, and more than 70 foods have been reported as causing food allergies. There is no current treatment for food allergies, and avoidance of the causative food is the only recommended prevention method. Access to care is crucial with food allergy; without it, the reaction can lead to inflammation of the airways, restricted breathing, and subsequent death.

Many food allergies begin in childhood. Children develop allergies in order of their exposure to the causative agent, so food allergies begin when food is introduced into the diet. Food allergy can develop from a combination of genetic factors and environmental exposures, as part of overall atopy, a genetic predilection toward overreactive immune responses against harmless environmental exposures. Many people outgrow their food allergies, although many of the most serious allergies are lifelong.

Food allergies are not the same as intolerance, which can cause abdominal cramping, but is not associated with an allergic response mediated by immunoglobulin E (IgE). The most common foods that trigger food allergies are eggs, fish, peanuts, soybeans, milk, tree nuts, gluten, and shellfish/crusta-ceans, and it is usually a protein in the food that acts as the allergen. Because foods that trigger allergy depend on exposure, food allergies vary across the world. In central Europe, allergy to celery is common, whereas east Asia has a substantial population with rice allergy.

As in any other allergic reaction, a person must be previously sensitized to the particular allergen, so that the immune system is able to identify and memorize a specific molecular “footprint” for each allergen. On encountering the allergen for the first time, IgE is produced. Once IgE has been synthesized, a second exposure to the allergen induces IgE to cause release of many inflammatory molecules. The signs and symptoms of an allergic food reaction can include tongue swelling, hives, difficulty breathing, vomiting, diarrhea, eczema, sudden decrease in blood pressure, loss of consciousness, and death.

Most symptoms are classified according to the organ system they affect. Gastrointestinal signs can include vomiting, pain, or diarrhea and can develop rapidly after consumption of the allergen. Oral allergy syndrome is a result of cross-sensitivity to foods that also cause allergic rhinitis in the individual; it manifests as itchy, swelling lips and tongue. Atopic dermatitis, or eczema, can be caused by food allergy, as can hives and angioedema, or deep tissue inflammation.

The most severe result of food allergy is anaphylaxis. The annual incidence of anaphylactic reactions is about 30 per 100,000 persons, and individuals with asthma, eczema, or hay fever are at greater relative risk of experiencing anaphylaxis. There are other causes of anaphylaxis besides food allergy, including medication allergy, insect stings, and latex, but foods [Page 671]are a common cause of anaphylaxis. Anaphylaxis is a systemic reaction that can affect several organ systems at the same time and can be life threatening without immediate treatment. An anaphylactic reaction may begin with a tingling or itching sensation in the mouth, and progress to hives, swelling of the mouth and throat area, difficulty breathing, vomiting, diarrhea, abdominal cramping, and loss of consciousness. The main treatment for an anaphylactic food response is injection with epinephrine or adrenaline. This can be self-administered with an EpiPen®, which is designed to inject a controlled amount of drug. The epinephrine constricts the swollen blood vessels and decreases inflammation, to decrease hives, tongue, throat and airway constriction, and to restore normal blood pressure.

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