Food allergy

Alternative names:

allergy to food; food hypersensitivity

Definition:

Symptoms that develop because of an immune response that is triggered by certain foods.

Causes, incidence, and risk factors:

Normally, the immune response defends against potentially harmful substances such as bacteria, viruses, and toxins. Occasionally, an immune response will be triggered by a substance (allergen) that is generally harmless and the person will develop an allergy.

The cause of food allergies is not fully understood, because they can produce such a variety of symptoms. The incidence is difficult to assess, because reporting is sporadic. Reactions to foods may vary from mild to fatal depending on the type and the severity of the reaction.

Food allergy is common. The immune system releases antibodies and substances including histamine in response to ingestion of a particular food or food component. The symptoms may be localized to the stomach and intestines, or may involve many parts of the body after the food is digested or absorbed. The symptoms usually begin immediately, seldom more than 2 hours after eating.

Food allergies often resemble other conditions such as food intolerance (caused by lack of the enzyme needed to digest that food), irritable bowel syndrome, response to emotional or physical stress, food contamination by toxins (food poisoning), and other disorders. A food allergy is distinguished from food intolerance and other disorders by the production of antibodies and the release of histamine and similar substances.

Asthma, eczema, or other disorders may be triggered or worsened by food allergies.

These foods more frequently cause a range of allergies -- anaphylaxis, hives, and asthma:

• shellfish (shrimp, crab, and lobster)
• nuts
• peanuts and peanut oil
• fruits (melons, strawberries, pineapple, and other tropical fruits)
• tomatoes
• food additives including dyes, thickeners, and preservatives

Foods that more frequently cause malabsorption syndromes include:

• wheat and other gluten-containing grains (see celiac disease)
• cow's milk protein (milk intolerance and intolerance of dairy products)
• corn products

Approximately 40% of Americans believe they have food allergies, while in reality fewer than 1% have true allergies. Most of the others involve symptoms caused by food intolerances or other disorders. Children more often have food allergies, and most will outgrow the food allergy.