Food allergy: Overview, Causes

Alternate Names : Allergy to food

Definition

A food allergy is an exaggerated immune response triggered by eggs, peanuts, milk, or some other specific food.

Overview, Causes, & Risk Factors

Normally, your body’s immune system defends against potentially harmful substances, such as bacteria, viruses, and toxins. In some people, an immune response is triggered by a substance that is generally harmless, such as a specific food.

The cause of food allergies is related to your body making a type of allergy-producing substance called immunoglobulin E (IgE) antibodies to a particular food.

Although many people have a food intolerance, food allergies are less common. In a true food allergy, the immune system produces antibodies and histamine in response to the specific food.

Any food can cause an allergic reaction, but a few foods are the main culprits. In children, the most common food allergies are to:

* Eggs
* Milk
* Peanuts
* Shellfish (shrimp, crab, lobster, snails, clams)
* Soy
* Tree nuts
* Wheat

A food allergy frequently starts in childhood, but it can begin at any age. Fortunately, many children will outgrow their allergy to milk, egg, wheat, and soy by the time they are 5 years old if they avoid the offending foods when they are young. Allergies to peanuts, tree nuts, and shellfish tend to be lifelong.

In older children and adults, the most common food allergies are:

* Fish
* Peanuts
* Shellfish
* Tree nuts

Food additives — such as dyes, thickeners, and preservatives – may rarely cause an allergic or intolerance reaction.

An oral allergy syndrome may occur after eating certain fresh fruits and vegetables. The allergens in these foods are similar to certain pollens. Examples are melon/ragweed pollen and apple/tree pollen.

Many Americans believe they have food allergies, while in reality fewer than 1% have true allergies. Most people’s symptoms are caused by intolerances to foods such as:

* Corn products
* Cow’s milk and dairy products (See: Lactose intolerance)
* Wheat and other gluten-containing grains (See: Celiac disease)

Pictures & Images

Food guide pyramid

The U.S. Department of Agriculture’s newest food pyramid guide, called MyPyramid, encourages consumers to make healthier food choices and to get regular exercise. Unlike the older model, food groups are arranged in vertically bands, instead of horizontal ones. Band width indicates portion size. The wider the band, the more food from that group you should eat.

Anaphylaxis

Anaphylaxis

Anaphylaxis is an acute systemic (whole body) type of allergic reaction which occurs when a person has become sensitized to a certain substance or allergen and is again exposed to the allergen. Some drugs, such as those used for pain relief or for X-rays, may cause an anaphylactoid reaction on first exposure. Histamines and other substances released into the bloodstream cause blood vessels to dilate and tissues to swell. Anaphylaxis may be life-threatening if obstruction of the airway occurs, if blood pressure drops, or if heart arrhythmias occur.

Food allergies

Food allergies

The body’s immune system normally reacts to the presence of toxins, bacteria or viruses by producing a chemical reaction to fight these invaders. However, sometimes the immune system reacts to ordinarily benign substances such as food or pollen, to which it has become sensitive. This overreaction can cause symptoms from the mild (hives) to the severe (anaphylactic shock) upon subsequent exposure to the substance. An actual food allergy, as opposed to simple intolerance due to the lack of digesting enzymes, is indicated by the production of antibodies to the food allergen, and by the release of histamines and other chemicals into the blood.

Read food labels

Read food labels

Allergic reactions to a certain food can include diffuse hives, hoarse voice, wheezing, and, in severe reactions, low blood pressure and closing down of the windpipe. Medications such as antihistamines and skin creams may provide some relief from itching and rashes, but the best way to prevent future allergic reactions is to avoid the offending food in the first place. Reading the labels contained on most products is a useful way to find a certain food that a person may want to avoid.

Dermatitis, perioral

Dermatitis, perioral

Dermatitis around the mouth (perioral) is most common in young to middle age women. Frequently, no specific cause is found. However, there appears to be an association with fluorinated steroids. In children, dermatitis around the mouth may be associated with irritation from specific foods or other materials carried to the face on the hands.

Antibodies

Antibodies

Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy substances containing antigens.

Food allergy: Overview, Causes

Food allergy: Symptom & Signs, Diagnosis & Tests

Food allergy: Treatment


Review Date : 11/15/2009
Review Date : 4/23/2009
Reviewed By : Stuart I. Henochowicz, MD, FACP, Associate Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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