Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

A food allergy is a reaction by the body's immune system to something in a food, usually a protein; the body mistakenly acts like it is a germ or some other invader, and does its best to defend itself.

While any food could possibly cause an allergy, certain foods are much more likely to do so. In children, the foods that most commonly cause allergic reactions are:

  • Peanuts

  • Eggs

  • Milk

  • Soy

  • Wheat

  • Shellfish

  • Tree nuts

Most allergic reactions occur within 30 minutes of consuming the problem food. Often, the reaction occurs within 5 to 10 minutes, but it can occur as long as 4 to 6 hours after ingestion.

Food allergy is different from food intolerance. In food intolerance, there is a physical reaction to a food, but that reaction isn't allergic. Lactose intolerance is a common example; people who suffer from this have trouble digesting one of the sugars in milk and can have stomachaches or diarrhea when they drink milk or eat dairy products. While the symptoms of food intolerance can be uncomfortable, this condition is not dangerous. There are also other conditions, such as celiac disease, which can cause reactions to foods (people with celiac disease have trouble with anything containing wheat) that are not allergic.

Another form of allergy is called the oral allergic syndrome. People who have this get itching of the lips, mouth, and throat (and sometimes swollen lips) after eating certain fruits or vegetables. This is rarely dangerous. Food allergies are becoming more common, especially among children. Experts estimate that up to 8 percent of children suffer from food allergy. In adults, that number is 1 percent to 2 percent. While the exact cause of food allergy is unknown, it does tend to run in families.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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