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Symptoms that develop because of an exaggerated immune response that is triggered by certain foods. Alternative Names Food hypersensitivity; Allergy to food 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: - shellfish (shrimp, crab, and lobster)
- nuts
- peanuts (not a true nut) and peanut products
- fruits (melons, strawberries, pineapple, and other tropical fruits)
- tomatoes
- food additives including dyes, thickeners, and preservatives
Foods that more frequently cause malabsorption or other food intolerance syndromes include: - wheat and other gluten-containing grains (see celiac disease)
- cow's milk (milk/lactose intolerance and intolerance of dairy products)
- corn products
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. Prevention 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. Symptoms These symptoms may follow ingestion of the offending food(s): - scratchy throat
- anaphylaxis (which may result in death)
- abdominal pain
- diarrhea
- nausea
- vomiting
- stomach cramps
- itching of the mouth, throat, eyes, skin, or any area
- hives (urticaria)
- angioedema (swelling of the eyelids, face, lips, and tongue)
- light-headedness, fainting
- nasal congestion
- a runny nose (rhinitis)
- shortness of breath
- wheezing
- difficulty swallowing
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
- skin tests, though rarely used today
- Presence in the blood of specific antibodies to allergen (RAST test)
2011-10-24
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