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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.

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If you are highly sensitive to a certain food, you may have an allergic reaction simply by being near where the food was prepared or served.

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.


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.

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