Food Allergy

Food allergy causes a variety of allergic symptoms including hives, vomiting, diarrhea and life-threatening anaphylaxis, usually within minutes and occasionally up to an hour after eating.  Reactions attributed by some to food that are delayed for many hours or days after ingestion of a food are difficult to prove as genuine food allergy. Immune mechanisms to explain apparently delayed reactions have been proposed, but remain theoretical. Food allergy is common in children with atopic dermatitis and may aggravate the skin disease.  

Some people have an itching sensation in the mouth and throat occurring at the instant that certain fresh vegetables or certain types of fresh fruit are eaten. This generally benign condition is known as the oral allergy syndrome. 

It is uncommon for food allergy to cause nasal symptoms or attacks of asthma (unless the allergy is severe):  the vast majority of patients with allergic rhinitis or asthma DO NOT have food allergy. Most people who think they are allergic to foods but do not know which food to suspect cannot be proven to have food allergy when tested by blinded food ingestion tests.  Unlike food poisoning from contaminated food, allergic reactions to food are repeatable when the suspect food is eaten again.

Gastric and/or intestinal reactions to dairy products may be caused by lactose intolerance, which is not an allergic problem.  Chronic diarrhea and poor absorption of food can be caused by intolerance to gluten, a component of wheat, rye and barley.  This is not a typical food allergy, and is causeed in part by a toxic reaction to gluten.  Some patients seem to sense more mucus in their throat after drinking whole cow's milk, but this non-serious condition, also not allergy, resolves with drinking skim milk and has not been proven to aggravate respiratory disease.

Genuine food allergy does occur commonly in infants, usually involving dairy products, soybean products, or egg.  These allergies are usually outgrown by the age of 3 years, but require dietary exclusion in infancy to prevent symptoms that can be severe at that age. 

Allergy to certain foods, especially peanut, can be life threatening, particularly in patients who also have asthma.   Food allergy of this severity requires strict avoidance measures, and the constant availability of emergency epinephrine injection kits and liquid antihistamine.  In these patients the allergy may be a life-long problem.

Skin tests may confirm the identity of foods causing rapid-onset reactions.  Falsely positive tests to foods are often found in patients who are able to eat those foods with no reaction.   Skin testing for foods in patients who do not know which foods to suspect is usually difficult to interpret without undergoing critical evaluation of the results of elimination and closely observed ingestion of suspect foods.  Blood tests for food based on methods to identify IgE antibodies (often referred to as RAST) can provide similar information to skin testing, but some laboratories claim to diagnose food allergy using tests that have never been scientifically validated.  Food allergy in infants young children is not always mediated by IgE antibodies and therefore some children with food reactions may have negative skin tests and blood tests.

In general, if you do not think you have food allergy, it is preferable not to be tested for it.

Treatment of food allergy is mainly limited to avoidance of the food that caused the reaction.  In children the allergy often improves over time to the point that the food can be eaten again, at least in small quantities.  Allergen immunotherapy to foods is ineffective and may be dangerous.

Further Reading
Food Allergy Network FAQ
NIAID: Food Allergy
AAAAI: Food Allergy
AAAAI: Work Group Report. Adverse Reactions to Foods, 2003
Sampson HA: Food Allergy. Journal of Allergy & Clinical Immunology Vol 111 (2 Suppl), pp S540-S547, 2003.
Sicherer SH, Sampson HA. 9. Food allergy [Review]. Journal of Allergy & Clinical Immunology Vol 117 (2 Suppl Mini-Primer): pp S470-5, 2006 Feb.
 

Disclaimer:   This site is for educational purposes only.  Any information that you have found in this web site is not intended to replace medical care or advice given to you by your own physicians. You should consider consulting your local medical library and other web sites for additional information. 

Comments and suggestions welcome!   Email: schumach@u.arizona.edu
Content Owner:  Michael J. Schumacher, MB, FRACP, The University of Arizona

Updated 7/2008