Print Page
Allergy Overview

Allergies are diseases of the immune system that cause an overreaction to substances called "allergens." Allergies are grouped by the kind of trigger, time of year or where symptoms appear on the body: indoor and outdoor  allergies (also called "hay fever," "seasonal," "perennial" or "nasal" allergies), food allergies, latex allergies, insect  allergies, skin  allergies and eye  allergies. People who have allergies can live healthy and active lives.

movie Multimedia
Glossary Glossary of Allergy Terms



If you break out in hives when a bee stings you, or you sneeze every time you pet a cat, you know what some of your allergens are. But if the pattern is not so obvious, try keeping a record of when, where, and under what circumstances your reactions occur. This can be as easy as jotting down notes on a calendar. If the pattern still isn't clear, make an appointment with your doctor for help.

Doctors Diagnose Allergies in Three Steps:

  • Personal and medical history. Your doctor will ask you questions to get a complete understanding of your symptoms and their possible causes. Bring your notes to help jog your memory. Be ready to answer questions about your family history, the kinds of medicines you take, and your lifestyle at home, school, and work. For example, if you've ever been treated for allergies in the past you're more likely than other to have allergies later in life, too.

  • Physical examination. If your doctor suspects an allergy, he/she will pay special attention to your ears, eyes, nose, throat, chest, and skin during the physical examination. This exam may include a pulmonary function test to detect how well you exhale air from your lungs. You may also need an X-ray of your lungs or sinuses.

  • Tests to determine your allergens. Your doctor may do a skin test, patch test or blood test.

Skin test. For most people, skin tests are the most accurate and least expensive way to confirm suspected allergens. There are two types of allergen skin tests. In prick/scratch testing, a small drop of the possible allergen is placed on the skin, followed by lightly pricking or scratching with a needle through the drop. In intra-dermal (under the skin) testing, a very small amount of allergen is injected into the outer layer of skin.

With either test, if you are allergic to the substance, you will develop redness, swelling, and itching at the test site within 20 minutes. You may also see a "wheal" or raised, round area that looks like a hive. Usually, the larger the wheal, the more sensitive you are to the allergen.

Patch test. This test determines if you have contact dermatitis. Your doctor will place a small amount of a possible allergen on your skin, cover it with a bandage, and check your reaction after 48 hours. If you are allergic to the substance, you should develop a rash.

Blood tests. Allergen blood tests (also called radioallergosorbent tests [RAST], enzyme-linked immunosorbent assays[ELISA], fluorescent allergosorbent tests [FAST], multiple radioallergosorbent tests [MAST], or radioimmunosorbent tests [RIST]) are sometimes used when people have a skin condition or are taking medicines which interfere with skin testing. Your doctor will take a blood sample and send it to a laboratory. The lab adds the allergen to your blood sample, and then measures the amount of antibodies your blood produces to attack the allergens.


Also learn more about allergy diagnosis from the American College of Asthma, Allergy & Immunology (ACAAI).

SOURCE: This information should not substitute for seeking responsible, professional medical care. First created 1995; updated 2011.
© Asthma and Allergy Foundation of America (AAFA) Editorial Board

© Asthma and Allergy Foundation of America
www.aafa.org 1-800-7-ASTHMA