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.

No one knows why some people develop them, but heredity seems to play a role. Allergies may flare up and subside throughout your life. The 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 cannot tell the good from the bad 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. Some of 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

Allergies come in many distinct forms and are typically grouped in general categories according to the types of substances that cause them or the parts of the body they affect.

Skin allergies: Eczema -- also called contact or atopic dermatitis -- is caused by direct, skin exposure to a specific allergen; atopic dermatitis has no known cause, but it is usually hereditary. Hives, or urticaria, is an eruption of itchy, swollen, reddened welts that can last for minutes or days. Angioedema is characterized by a deeper swelling around the eyes and lips, and sometimes of the hands and feet as well. Both hives and angioedema stem from the body's adverse reaction to certain foods, pollen, animal dander, drugs, insect stings, cold, heat, light, or even emotional stress.

Respiratory allergies: Approximately 20 million Americans suffer from hay fever (allergic rhinitis), which frequently also causes bouts of sinusitis. Typical symptoms include itchy eyes, nose, roof of mouth, or throat, along with nasal congestion, coughing and sneezing. If you (or members of your family) have other allergies such as dermatitis or asthma, you are more likely to have hay fever. Hay fever can be caused by a number of difference substances -- pollens of ragweed, grasses, and other plants whose pollen is spread by the wind, molds, dust, and animal dander (dead skin scales and saliva). Mold allergies are caused by spores in the air. Outdoor molds thrive in warm seasons or climates, while indoor molds grow year round in damp locations (basements and bathrooms, for example). Dust causes allergies because it harbors offenders such as pollen, mold spores, and microscopic dust mites; it may also contain irritating fibers from fabrics, upholstery, and carpets.