Imagine what it would be like if eating a peanut butter sandwich or some shrimp, or drinking a tall glass of milk left you vomiting, gasping for breath, and furiously scratching a fresh crop of hives. For some people with food allergies, that's reality.

A food allergy, or hypersensitivity, is an abnormal response to a food triggered by the immune system. While many people often have gas, bloating or another unpleasant reaction to something they eat, this is not an allergic response. Such a reaction is thought to not involve the immune system and is called "food intolerance."

Only about 1.5 percent of adults and up to 6 percent of children younger than 3 years in the United States — about 4 million people — have a true food allergy, according to researchers who have examined the prevalence of food allergies.

It's critical for people who have food allergies to identify them and to avoid foods that cause allergic reactions. Some foods can cause severe illness and, in some cases, a life-threatening allergic reaction (anaphylaxis) that can constrict airways in the lungs, severely lower blood pressure, and cause suffocation by the swelling of the tongue or throat.

An estimated 150 Americans die each year from severe allergic reactions to food, says Hugh A. Sampson, M.D., director of the Elliot and Roslyn Jaffe Food Allergy Institute at Mount Sinai School of Medicine in New York City and a food allergy expert.

The Food and Drug Administration's Center for Food Safety and Applied Nutrition has made it a high priority to boost consumer and food industry awareness of food allergens. As part of these efforts, the FDA is conducting food allergen education programs for consumers and industry. The agency also is developing a strategy for clear, easy-to-understand labeling of food allergens.

Allergic Reactions

Food normally doesn't provoke a response from the human immune system, the body's defense against microbes and other threats to health. In food allergies, two parts of the immune response are involved, according to researchers at the National Institute of Allergy and Infectious Diseases. One is the production of an antibody called immunoglobulin E (IgE) that circulates in the blood. The other part is a type of cell called a mast cell. Mast cells occur in all body tissues but especially in areas that are typical sites of allergic reactions, including the nose, throat, lungs, skin, and gastrointestinal tract.

People usually inherit the ability to form IgE against food. Those more likely to develop food allergies come from families in which allergies such as hay fever, asthma, or eczema are common.

A predisposed person must first be exposed to a specific food before IgE is formed. As this food is digested for the first time, tiny protein fragments prompt certain cells to produce specific IgE against that food. The IgE then attaches to the surface of mast cells. The next time the particular food is eaten, the protein interacts with the specific IgE on the mast cells and triggers the release of chemicals such as histamine that produce the symptoms of an allergic reaction.

If the mast cells release chemicals in the nose and throat, the allergic person may experience an itching tongue or mouth and may have trouble breathing or swallowing. If mast cells in the gastrointestinal tract are involved, the person may have diarrhea or abdominal pain. Skin mast cells can produce hives or intense itching.

The food protein fragments responsible for an allergic reaction are not broken down by cooking or by stomach acids or enzymes that digest food. These proteins can cross the gastrointestinal lining, travel through the bloodstream and cause allergic reactions throughout the body.

The timing and location of an allergic reaction to food is affected by digestion. For example, an allergic person may first experience a severe itching of the tongue or "tingling lips." Vomiting, cramps or diarrhea may follow. Later, as allergens enter the bloodstream and travel throughout the body, they can cause a drop in blood pressure, hives or eczema, or asthma when they reach the lungs. The onset of these symptoms may vary from a few minutes to an hour or two after the food is eaten.

Most Likely Suspects

Food allergy patterns in adults differ somewhat from those in children. The most common foods to cause allergies in adults are shrimp, lobster, crab, and other shellfish; peanuts (one of the chief foods responsible for severe anaphylaxis); walnuts and other tree nuts; fish; and eggs.

In children, eggs, milk, peanuts, soy and wheat are the main culprits. Children typically outgrow their allergies to milk, egg, soy and wheat, while allergies to peanuts, tree nuts, fish and shrimp usually are not outgrown.

Adults usually do not lose their allergies.

Tags: Allergies

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