Step 1: What is an Allergy?

Return to Index Step 1: What is an Allergy?Step 2: The Role of the Immune System Step 3: What Substances Cause Allergies?Step 4: Allergy-Related Conditions Step 5: Should You See an Allergist?Step 6: Allergy Testing and Diagnosis Step 7: Introduction to Allergy Treatment Step 8: Avoid Allergy Triggers Step 9: Types of Allergy Medication Step 10: Over-the-Counter vs Prescription Drugs Step 11: Immunotherapy Step 12: You and Your Doctor Are a Team Key Points Glossary

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When most people think of an allergy, they think of the sneezing, congestion, and itchy eyes caused by pollen. In fact, allergies can be caused by just about any substance that you inhale or swallow, or which touches your skin.

Your body's immune system is designed to attack harmful substances like bacteria and viruses. But with allergies, your body launches an assault on substances that are basically harmless -- such as pollen, mold, dust mites, pet saliva and dander, and even medications and insect sting venom.

Allergies are extremely common. About 50 million Americans suffer from allergies, leading to a lot of missed work and school days each year. Annual medical costs exceed $4 billion.

Not only do allergies cause a range of annoying symptoms such as sneezing and itchy eyes, but they can aggravate or trigger other conditions such as asthma, sinusitis, and ear infections. For example, when allergies cause inflammation in your nasal passages, the opening to your sinuses can become blocked, leading to sinus inflammation, sinus infections, and sinus pain. Similarly, if allergies cause inflammation in your ear canal, the ears don't drain properly, which can lead to ear infections.

But allergies don't stop there. The body's immune system is active from your head to your toes: allergies can cause different skin-related symptoms (such as hives, eczema, and rashes); some types of allergies can lead to gastrointestinal problems; and assorted allergy-related symptoms can pervade the body (such as fatigue, headaches, loss of smell, and sleep disturbances).

One of the most deadly kinds of allergic reaction is called "anaphylaxis," which occurs when the entire body has a swift, severe reaction to something such as peanuts or bee stings. The body literally goes into shock, leading to a sharp drop in blood pressure, respiratory arrest, and possible heart failure.

To continue to the next step of the allergy guide, click "next" below.

Reference: American Academy of Allergy, Asthma and Immunology (AAAAI). The Allergy Report: Science Based Findings on the Diagnosis & Treatment of Allergic Disorders. 1996-2001.

Review Date: May 25, 2005
Reviewed By: Alan Greene, M.D., F.A.A.P., Department of Pediatrics, Packard Children's Hospital, Stanford University School of Medicine; Chief Medical Officer, A.D.A.M., Inc., and Jacqueline A. Hart, M.D., Department of Internal Medicine, Newton-Wellesley Hospital, Boston, Ma.

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