| Definition: |
Symptoms that develop because of an exaggerated immune response that is triggered by certain foods.
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| Alternative Names: |
Food hypersensitivity; Allergy to food
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| Causes, incidence, and risk factors: |
Normally, the immune response defends against potentially harmful substances such as bacteria, viruses, and toxins. Occasionally, an immune response will be triggered by a substance (allergen) that is generally harmless and the person will develop an allergy.
The cause of food allergies is not fully understood, because they can produce such a variety of symptoms. The incidence is difficult to assess, because reporting is sporadic. Reactions to foods may vary from mild to fatal depending on the type and the severity of the reaction as well as amount of allergen accidentally ingested.
While symptoms of food intolerance are common, true food allergy is less common. A food allergy is distinguished from food intolerance and other disorders by the production of antibodies and the release of histamine and similar substances. The immune system produces antibodies and substances including histamine in response to ingestion of a particular food or food component. The symptoms may be localized to the stomach and intestines, or may involve many parts of the body after the food is digested or absorbed. The symptoms usually begin immediately, seldom more than 2 hours after eating.
Asthma, eczema, or other disorders may be triggered or worsened by food allergies.
These foods more frequently cause a range of allergies -- anaphylaxis, hives, and asthma:
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shellfish (shrimp, crab, and lobster)
- nuts
- peanuts (not a true nut) and peanut products
- fruits (melons, strawberries, pineapple, and other tropical fruits)
- tomatoes
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food additives including dyes, thickeners, and preservatives
Foods that more frequently cause malabsorption or other food intolerance syndromes include:
Approximately 40% of Americans believe they have food allergies, while in reality fewer than 1% have true allergies. Most of the others involve symptoms caused by food intolerances or other disorders. Children more often have food allergies, and most will outgrow the food allergy.
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| Symptoms: |
These symptoms may follow ingestion of the offending food(s):
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| Signs and tests: |
A history of typical symptom development shortly after contact with a suspect food or food additive is highly suspicious of food allergy. Clinical signs can include diffuse hives, hoarse voice, wheezing, and, in severe reactions, low blood pressure and airway closure (closing down of the windpipe).
Antibody (immunoglobulin, particularly IgE) levels that are elevated confirm the presence of an allergy.
The food causing the allergy can sometimes be identified by:
- elimination diets (The suspected food is eliminated from the diet until the symptoms disappear, then reintroduced to see if allergic reaction develops. This method is not foolproof but may be used to narrow the list of suspected foods.)
- food provocation diet
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skin tests, though rarely used today
- Presence in the blood of specific antibodies to allergen (RAST test)
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| Treatment: |
Treatment varies with the severity and type of symptoms. The goals of treatment are reduction of symptoms and avoidance of future allergic reactions.
Mild or localized symptoms may require no treatment. The symptoms will subside in a brief time. Antihistamines may relieve the discomfort of many symptoms. Soothing skin creams may provide some relief of rashes. Severe reactions require treatment with epinephrine (adrenaline) by injection, as soon as possible after symptoms develop. Self-administration of epinephrine is routinely taught to food allergy sufferers and can be life saving. Avoiding the offending food is the best way to prevent future allergic reactions.
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| Support Groups: |
General and up-to-date information for food allergy sufferers can be obtained online through the Food Allergy and Anaphylaxis Network.
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| Expectations (prognosis): |
Food allergies may cause symptoms that range from mild abdominal discomfort to life-threatening anaphylaxis. The avoidance of offending foods may be easy if the food is uncommon or easily identified. However, the successful avoidance of offending foods may involve a severely restricted diet and often requires strict reading of all package ingredients and detailed inquiries when eating away from home. Children may outgrow food allergies.
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| Complications: |
- discomfort due to an allergic reaction and its treatment
- reduced social interactions with a restricted diet
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anaphylaxis (life-threatening allergic reaction)
- rarely, malnutrition in an infant with multiple food allergies
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| Calling your health care provider: |
Call your health care provider if the symptoms of allergy develop after eating, particularly if audible wheezing, difficulty breathing, or other symptoms occur. If you have been prescribed epinephrine to give yourself for a reaction, this should be done as soon as possible, even prior to calling the doctor if you have severe reactions.
Go to the emergency room or dial the local emergency number (911) if the symptoms become so severe that your ability to breathe is threatened.
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| Prevention: |
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Breastfeeding helps to prevent allergies. Otherwise, there is no known prevention of food allergies except to delay the introduction of allergy-causing foods to infants until the gastrointestinal tract (GI tract) has had a chance to mature. The timing for this varies from food to food and from baby to baby.
Once an allergy has developed, carefully avoiding the offending food usually prevents further problems.
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Review Date: 11/20/2001
Reviewed By: Alan Greene, M.D., Chief Medical Officer of A.D.A.M., and Frederic F. Little, M.D., Department of Allergy and Pulmonary/Critical Care Medicine, Boston University School of Medicine, Boston, MA. Review provided by VeriMed Healthcare Network.
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