Real Allergy Causes

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Food allergies afflict perhaps 2-2.5% of the U.S. population or 6-7 million individuals. The symptoms can range from comparatively mild reactions such as hives, itching, and gastrointestinal distress to life-threatening reactions such as laryngeal edema (throat swelling), asthma, and anaphylactic shock. An estimated 29,000 Americans visit emergency rooms each year as the result of inadvertent ingestion of foods to which they are allergic; an estimated 150-200 deaths from food allergies occur each year in the U.S. also.

Eight foods or food groups (the so-called Big 8) are responsible for 90% of all food allergies in the U.S. and on a worldwide basis. These foods are peanuts, crustacean shellfish (shrimp, crab, lobster), milk, eggs, fish, tree nuts (almonds, walnuts, hazelnuts, etc.), soybeans, and wheat. This list was established by the Codex Alimentarius Commission in Rome in 1999 with worldwide input. Some countries have added one or more other foods. For example, Canada includes sesame seeds on its list of commonly allergenic foods. Virtually any food that contains protein can be allergenic at least on a rare basis. Some foods are noteworthy because they cause severe reactions on occasion even though they are less frequently implicated in food allergies than the foods included in the Big 8. Those foods would include sesame seeds, molluscan shellfish (clams, oysters, scallops, etc.), sunflower seeds, and cottonseed.

Regional differences can occur in the frequency of allergic reactions to specific foods. Codfish allergy appears to be more common in Scandanavian countries than it is in the U.S.

Although virtually any allergenic food can cause a severe reaction if consumed in sufficient amounts by a highly sensitized individual, the majority of severe reactions is caused by peanuts, tree nuts, and crustacean shellfish. Peanuts and tree nuts are a particularly problem because they can be difficult to identify when used in formulated foods.

The Big 8 are the foods most frequently involved in systemic and potentially severe allergies. However, the most frequent food allergy of all may be oral allergy syndrome (OAS). OAS involves typically very mild symptoms such as hives or itching occurring around the mouth. Many people experiencing OAS do not even realize that they have a food allergy. OAS tends to occur with various fresh fruits and vegetables including celery, apples, carrots, peaches and watermelon. These individuals are sensitized to airborne pollens, and the individuals react when the allergens in the pollens interact with foods containing certain proteins. Reactions usually only occur in or near the mouth because these proteins are easily destroyed by stomach acid and digestion; they are also easily destroyed by heat processing. A common example of OAS in the U.S. is a reaction to watermelon in individuals with ragweed allergy.

Many consumers believe that they have food allergies. However, before avoiding the suspect foods, it is prudent to seek a confirmatory diagnosis by an allergist. Avoidance is obviously more important in situations involving severe reactions.

Steve Taylor, Ph.D., Professor and Co-Director, Food Allergy Research & Resource Program, University of Nebraska, Lincoln, NE