Food Allergy What Is an Allergic Reaction to Food?

A food allergy occurs when the immune system responds to a harmless food as if it were a threat. The first time a person with food allergy is exposed to the food, no symptoms occur. But the body has been now been primed, and when the person eats the food again, an allergic response occurs.

An allergic reaction to food usually takes place within a few minutes to several hours after exposure to the allergen. The process of eating and digesting food and the location of immune cells involved in the allergic reaction process both affect the timing and location of the reaction.

© iStockphoto On this page: Allergic reaction process Symptoms of food allergy First exposure to food Cross-reactive food allergies Allergic Reaction Process

An allergic reaction to food is a two-step process:

Step 1:

The first time you are exposed to a food allergen, your immune system makes specific immunoglobulin E (IgE) antibodies to that allergen. IgE antibodies circulate through your blood and attach to types of immune cells called mast cells and basophils. Mast cells are found in all body tissues, especially in your nose, throat, lungs, skin, and GI(gastrointestinal) tract. Basophils are found in your blood and also in tissues that have become inflamed because of an allergic reaction.

Step 2:

The next time you are exposed to the same food allergen, the allergen binds to the IgE antibodies that are attached to the mast cells and basophils. The binding signals the cells to release massive amounts of chemicals such as histamine.

Depending on the tissue in which they are released, these chemicals will cause you to have various symptoms of food allergy. The symptoms can range from mild to severe. A severe allergic reaction can include a potentially life-threatening reaction called anaphylaxis.

Generally, you are at greater risk for developing a food allergy if you come from a family in which allergies—including food allergies and other allergic diseases such as asthma or eczema—are common. Having two parents who have allergies makes you more likely to develop food allergy than someone with one parent who has aller

Symptoms of Food Allergy

If you are allergic to a particular food, you may experience some or all of the following symptoms:

Itching in your mouth or swelling GI symptoms, such as vomiting, diarrhea, or abdominal cramps and pain Hives or eczema Tightening of the throat and trouble breathing Drop in blood pressure

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First Exposure to Food

Usually, you are first exposed to a food when you eat it but sometimes a first exposure or subsequent exposure can occur without your knowledge.

This may be true in the case of peanut allergy. A person who experiences anaphylaxis on the first known exposure to peanut may have previously had contact with peanuts in any of the following ways:

Touching peanuts Using a peanut-containing skin care product Breathing in peanut dust in the home or when close to other people eating peanuts Cross-reactive Food Allergies

If you have a life-threatening reaction to a certain food, your healthcare professional will show you how to avoid similar foods that may trigger this reaction. For example, if you have a history of allergy to shrimp, allergy testing may show that you are also allergic to other shellfish, such as crab, lobster, and crayfish. This is called cross-reactivity.