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Food Allergies - Cause

Food allergies occur when the body's immune system overreacts to substances in food you have eaten, triggering an allergic reaction. Food allergies are more common in young children than in adults.

  • Milk, eggs, peanuts, tree nuts, fish, shellfish, wheat, and soy cause most problems in children. Some babies are so sensitive to these foods that if the offending food is eaten by the mother, drinking her breast milk can cause a reaction. Most children outgrow allergies to eggs, milk, wheat, and soy.
  • Peanuts, tree nuts, fish, and shellfish cause most of the allergic reactions in teens and adults. Adults typically remain allergic to the food for life.

Food allergies are most common in people who are atopic, meaning they have an inherited tendency to have allergic conditions. These people are more likely to have asthma, various allergies, and a skin condition called atopic dermatitis. Asthma can make the reaction to a food more severe.

If you are highly sensitive to a particular food, you may have an allergic reaction by simply being near the food. Flying in airplanes where other passengers are eating peanuts or simply eating in a seafood restaurant may cause symptoms.

Because peanuts are used in so many foods, peanut allergy has increased in the United States. For more information, see the topic Peanut Allergy.

Celiac disease is an abnormal immune system reaction to gluten, a protein found in grains like wheat and rye. It damages the small intestine so that it can't do a good job of absorbing nutrients from your food. For more information, see the topic Celiac Disease.

Cross-reactivity

Many people, but not all people, are allergic to foods that are similar or somehow related. This is called cross-reactivity. For example, if you are allergic to shrimp, you may also be allergic to other shellfish, like crab or lobster. If you are allergic to peanuts, you may be allergic to other members of the legume family, such as peas and beans. You don't need to stop eating a cross-reactive food if you show no signs of an allergic reaction to it.

Oral allergy syndrome is a type of cross-reactivity. With this syndrome, people who have pollen allergies (such as a grass allergy) may develop itching, redness, and swelling of the lips and mouth when they eat fruits or vegetables that contain a protein that reacts with the pollen. These symptoms usually resolve quickly and do not involve other parts of the body.

Oral allergy syndrome usually involves a reaction to fresh fruits and raw vegetables:

  • If you are allergic to ragweed, your mouth may itch when you eat melons, especially cantaloupe.
  • If you are allergic to birch pollen, you may react to apple peels.

A growing number of people, especially health care workers, are discovering that they have an allergy to latex. Latex is the natural sap of the rubber tree. It is used in making surgical gloves, condoms, balloons, and other products. If you have a latex allergy, you may also have allergies to bananas, avocados, kiwi, and chestnuts.

Other concerns

Some people have allergic reactions to food after they exercise. This is called exercise-induced food allergy. As a person's body temperature rises with exercise, symptoms such as itching and lightheadedness start, sometimes leading to hives and even anaphylaxis, which can be deadly. To avoid exercise-induced food allergy, do not eat for a few hours before you exercise or right after exercising.

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WebMD Medical Reference from Healthwise

Last Updated: February 25, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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