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Southwestern United States
Information for patients with allergy and related problems
in the Southwest

Food Allergy

Food allergy causes a variety of allergic symptoms including hives, vomiting, diarrhea, cough and wheezing and life-threatening anaphylaxis, usually within minutes and occasionally up to an hour after eating.  It is caused by an aberrant response by the immune system to food proteins or similar molecules termed allergens which react with IgE antibodies specific for the food allergen.  The presence of IgE antibodies can be identified by allergy skin prick testing or by blood tests. 

Food allergy is commonly in infants, usually involving dairy products, soybean products, or egg.  These allergies are usually outgrown by the age of three years, but may require dietary exclusion in infancy to prevent symptoms that can be severe at that age.  Food allergy is common in children with atopic dermatitis and may aggravate the skin disease.  

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.

Anaphylaxis: Allergy to certain foods, especially peanut, can be life threatening, particularly in patients who also have asthma.  Anaphylaxis is a rapid (minutes or even seconds) onset of breathing difficulty and/or falling blood pressure and shock.  Food allergy of this severity requires strict avoidance measures, and the constant, immediate availability of emergency epinephrine injection kits (Epipen or the new and more convenient Auvi-Q).  Treatment includes self-injection with epinephrine and 2 teaspoons of liquid antihistamine such as Benadryl.  These patients should carry two epinephrine kits  at all times in case the first injection is ineffective.  The allergy may be a life-long problem.

Oral allergy syndrome:  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 and appears to be related to contact urticaria, a condition in which food allergens may trigger an immediate reaction on direct contact with skin. 

Gastrointestinal reactions:   Food allergy in infants and young children is not always mediated by IgE antibodies and therefore some children with reproducible food reactions may have negative skin tests and blood tests.  Vomiting, diarrhea and dehydration in infants in the first three months of life may be from food protein induced enterocolitis.  The food involved is usually cow's milk protein, but may also be soy, wheat, egg, rice and other foods.   Blood-stained stool in breast fed infants in the first three months of life may be from food protein-induced proctocolitis, which in some cases is caused by transmission of cow's milk or soy protein through breast milk.

In older children and and adolescents, chronic symptoms of gastro-esophageal reflux, gastritis with pain and vomiting, and weight loss may be caused by allergic eosinophilic esophagitis and allergic eosinophilic gastroenteritis. These are conditions in which the intestinal tract is infiltrated with eosinophils that mediate the allergic rection by damaging the lining of the esophagus or gut.  Skin prick testing and elimination of identified foods can eliminate symptoms over many weeks.

Lactose intolerance, not an allergic problem, causes gastric or intestinal reactions to dairy products and/including bloating, abdominal pain and diarrhea.    Some people who dislike milk sense mucus in their throat after drinking whole cow's milk.  This non-serious condition is also not allergy and does not affect the lower aiways.  It resolves with drinking skim milk.  Chronic diarrhea and poor absorption of food can be caused by intolerance to gluten, a component of wheat, rye and barley.  Although this problem known as celiac disease has immunologic features, it is not typical of common food allergy, and appears to be mainly a toxic reaction to gluten. 

Beliefs about food allergy:  The majority of patients with allergic rhinitis or asthma do not have food allergy.  However asthmatics who are very sensitive to certain foods may have severe asthmatic reactions after contacting the food.  People who think they are allergic to foods and yet do not have persistent gastrointestinal symptoms do not know which food to suspect. These individuals 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: the same or similar reaction occurs every time the food is eaten.

Testing for food allergy:  Skin prick tests may help to 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, objective 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 not been scientifically validated.  In general, if you do not think you have food allergy, and you do not have persistent and unexplained gastrointestinal symptoms, it is preferable not to be tested for it.

Treatment:  Treatment of food allergy is mainly limited to strict avoidance of the food that caused the reaction.  In children mild allergic reactions tend to improve over time to the point when the food can be eaten again, at least in small quantities.  Allergen immunotherapy to foods using available food extracts has not been proven to be effective and may be dangerous.

Travel with food allergy:  see AAAAI site Traveling with Allergies and Asthma

Further Reading
NIAID: Food Allergy Guidelines - What's in it for Patients
NIAID: Food Allergy Guidelines - Summary for Clinicians
AAAAI: Food Allergy
AAAAI:   Anaphylaxis
Food Allergy Network
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 2/2013