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| Definition |
| Symptoms that develop because of an 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.
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 (see celiac disease)
- 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.
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| 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
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| 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.ory
- food provocation diet
- skin tests - allergy
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