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Allergic Reaction Defined

An allergic reaction occurs when the immune system overreacts to a harmless substance known as an allergen.

The immune system protects the body from infections, viruses and diseases. In some people, substances such as pollen, certain foods, latex, mold, pet dander, dust mites or insect stings are allergens that trigger the production of antibodies called Immunoglobulin E (IgE). These antibodies travel to cells that release chemicals, causing symptoms most often in the nose, lungs, throat, sinuses, ears, lining of the stomach or on the skin.

The first time a person with an allergy is exposed to the allergen, it may not cause a reaction. However, the person is then sensitized to the allergen can and even minor future exposures to this allergen produce an allergic reaction.

Anaphylaxis (an-a-fi-LAK-sis) is a serious allergic reaction involving multiple parts of the body.

Learn more about allergy symptoms, diagnosis, treatment and management.

Video: What is an allergic reaction?