FOOD ALLERGY

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Alternative names

food hypersensitivity; allergy to food 

Definition

Symptoms that develop because of an immune response that is triggered by certain foods. 

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. 

Food allergy is common. The immune system releases 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. 

Food allergies often resemble other conditions such as food intolerance (caused by lack of the enzyme needed to digest that food), irritable bowel syndrome, response to emotional or physical stress, food contamination by toxins (food poisoning), and other disorders. A food allergy is distinguished from food intolerance and other disorders by the production of antibodies and the release of histamine and similar substances. 

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 and peanut oil
  •  fruits (melons, strawberries, pineapple, and other tropical fruits)
  •  tomatoes
  •  food additives including dyes, thickeners, and preservatives

Foods that more frequently cause malabsorption syndromes include:   

  • wheat and other gluten-containing grains
  • cow's milk protein (milk 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

There is no known way to prevent the development of a food allergy except the avoidance of highly allergenic foods in infants. Once an allergy has developed, strict avoidance of 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
  •  abdominal sounds (borborygmus, a gurgling or splashing sound heard over the intestine)
  •  diarrhea
  •  nausea
  •  vomiting
  •  stomach cramps
  •  a bloated feeling
  •  itching of the mouth, throat, eyes, skin, or any area
  •  hives (urticaria)
  •  angioedema (hives of the eyelids, lips, and so on)
  •  lightheadedness, fainting
  •  a headache
  •  nasal congestion
  •  a runny nose (rhinitis)
  •  shortness of breath
  •  wheezing
  •  difficulty swallowing

Signs and Tests

A history of symptom development shortly after contact with a suspect food or food additive is highly suspicious of food allergy. Listening to the lungs with a stethoscope (auscultation) may show wheezing.Antibody and/or 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 - allergy

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 symptoms may require treatment with corticosteroids (such as dexamethasone) or epinephrine (adrenalin). Avoiding the offending food is the best way to prevent future allergic reactions.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 avoidance of offending foods may involve a severely restricted diet and, in some cases, may result in malnutrition unless nutrients are supplemented. Children may outgrow food allergies. 

Complications

  •  discomfort
  •  reduced social interactions with a restricted diet
  •  anaphylaxis (life-threatening allergic reaction)

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.

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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