Allergies Health Center

Understanding Allergies -- the Basics

What Are Allergies?

The term allergy applies to an abnormal reaction by your immune system to a substance that is usually not harmful. Allergies come in a variety of forms and vary in severity from mildly bothersome to life-threatening. An estimated one-fifth of the Western Hemisphere's population suffers from allergies.

At this time, researchers are not sure what factors contribute to the development of allergies, but heredity seems to play a role. Allergies may flare up and subside throughout your life. A normally functioning immune system protects the body from foreign substances -- known as antigens -- by producing antibodies and other chemicals to fight against them. Usually the immune system ignores harmless substances, such as food, and fights only dangerous ones, such as bacteria. A person develops an allergic reaction when the immune system inappropriately reacts and releases chemicals like histamine to attack the harmless substance as if it were a threat. Histamine produces many of the symptoms associated with allergies. The hundreds of substances that may trigger allergic reactions range from pollen to pet dander to penicillin.

Most allergic reactions are not serious, but some, such as anaphylaxis, can result in an inability to breathe or a severe drop in blood pressure and can be fatal. Allergies can't be cured outright, but a variety of treatments are available to relieve the symptoms. If your allergy is severe, it is vital that you visit a doctor and get immediate treatment.

Types of Allergies

Allergic (or atopic) conditions come in many distinct forms and are typically grouped in general categories according to the types of reaction or the parts of the body they affect. Histamine and the protein antibody IgE are usually involved in immediate reactions; delayed reactions are typically identified as cell-mediated, primarily driven by immune cells.

Skin allergies: The cause of eczema -- also called atopic dermatitis -- is unknown. But it's thought that it's potentially caused by a combination of things including direct skin exposures to antigens, hereditary factors, impaired immune function, and disruption of the skin’s barrier function. Hives, or urticaria, is a rash consisting of an eruption of itchy, swollen, reddened welts that can last for minutes or days. Hives are not uncommon, affecting an estimated one in five people at some time in their lives. Angioedema is characterized by a deeper swelling in body tissues, typically around the eyes and lips, and sometimes of the hands, feet, or other parts of the body as well. Both hives and angioedema may stem from the body's adverse reaction to certain foods, pollen, animal dander, drugs, insect stings, cold, heat, light, or even emotional stress. Often, however, the cause may not be identified. Both of these reactions can occur in isolated cases and may not necessarily be an indicator of anaphylaxis. Chronic cases or cases of hives or angioedema complicated by other symptoms should be discussed with your physician.