Overview

Definition

Like clockwork, the sneezing and sniffling hits you every spring. Or maybe it's every fall. But chances are it's not a cold. You have allergies. So what are allergies? They are exaggerated reactions of the immune system to substances that in most people don't cause problems. Symptoms may be caused by different exposures such as a certain chemical affecting the skin, dust or pollen particles affecting the respiratory system, or particular foods affecting the stomach and intestines.

As many as 40 million to 50 million Americans may have allergies, according to the American Academy of Allergy, Asthma and Immunology. Allergies affect more than 20 percent of the U.S. population and allergic diseases are the sixth leading cause of chronic disease in the United States. And at least 35 million have seasonal allergic rhinitis, also known as hay fever.

Common allergens are pollen, molds, dust mites, animal dander, certain foods and medications, and latex.

Allergic rhinitis (AR), or hay fever, happens when an allergen is inhaled through the mouth or nose. Sometimes symptoms are year-round, meaning it could be triggered by dust mites, cockroaches, animal dander, pollen or mold spores. AR is the most common allergy and is considered a risk in developing asthma. Nearly 80 percent of people with asthma also have AR. Sinusitis is a common disease often triggered by AR. The condition is an acute or chronic inflammation of the nasal sinuses, the hollow cavities around the eyes and behind the nose. More than 15 percent of the U.S. population has this condition.

Eczema (atopic dermatitis). Eczema often happens when the allergen such as animal dander touches the skin. For 80 percent of people with the condition, symptoms started in childhood. More than 50 percent of sufferers develop asthma.

Hives (uritcaria) are caused by allergens such as foods, dust mites, pollens and animals. Medications include penicillin, sulfa, anti-seizure drugs, phenobarbital and aspirin.

Contact dermatitis. When skin contacts certain substances, usually a chemical, this condition may happen. Reaction may take hours or days to develop, as with poison ivy.

Allergic conjunctivitis is the most common eye allergy, occurring when airborne allergens get into the eye, irritating thin membranes covering the eyelids and the exposed surface of the eyes. Allergic conjunctivitis is in two forms: seasonal and perennial. The seasonal version is much more common, and is related to exposure to grass, tree and weed pollens and molds. The perennial form lasts throughout the year and can be triggered by dust mites, feathers or animal dander.

Food allergies may have severe and possibly life-threatening reactions, although this is not true for all people with food allergies. The most common triggers are cow's milk, eggs, peanuts, wheat, soy, fish, shellfish and tree nuts. Food allergies are more common in children and are increasing in prevalence. However, many children may outgrow certain allergies.

Anaphylaxis. Anaphylaxis is a rare, potentially fatal allergic reaction affecting many parts of the body at once. A trigger may be an insect sting, a food, such as nuts or shellfish, or medications. Usually the reaction is immediate and progresses within minutes. You must get to a hospital right away. About 150 to 200 people in the United States die each year from food-related anaphylaxis, the Food Allergy & Anaphylaxis Network reports.

Prognosis

Allergies do not have a cure, but they can be controlled effectively with good prevention, awareness of your triggers and knowing how to manage symptoms if they happen. If you cannot deal effectively with allergies on your own, a doctor can help.s

More on Allergies

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This article was reviewed and updated June 2007.