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What's the difference between a food allergy and a food intolerance?

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Updated May 15, 2009

Question: What's the difference between a food allergy and a food intolerance?
Answer: In practice, food allergies and food intolerances are usually treated in the same manner --- by avoiding the food that causes symptoms. But there are several differences in the way the body reacts to food in these two disorders that impacts patients:

  • Unlike allergies, most intolerances are not caused by an immune system response but by a reaction in the digestive tract. Because of this, it can be difficult to treat an accidental exposure to a substance one is intolerant to. (Benadryl and other allergy drugs will usually have no effect on an intolerance because most allergy drugs are antihistamines, and intolerances are not caused by histamine release).
  • Food intolerances are often less severe than food allergies --- in many cases, in fact, intolerant individuals can eat small amounts of the food they are intolerant of without ill effect. Lactose intolerance is a familiar example; many people with lactose intolerance find they can eat one serving of dairy products every other day or so without ill effect.
  • Food intolerances, unlike allergies, do not require a first exposure to a food to "prime" them.
  • Intolerances manifest a wide variety of symptoms. Many are gastrointestinal, though some may be fatigue, headaches, and "brain fog" --- feeling muddled in thought. Intolerances, however, do not cause hives or other allergy symptoms.
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