Allergies are a common and chronic condition that involves the body's immune system.

Normally, your immune system works to fight off viruses, bacteria, and other infectious

agents. When you have an allergy, your immune system treats a harmless substance, like dust

or pollen, as a threat. To fight this perceived threat, your immune system makes antibodies

called immunoglobulin E (IgE).

Substances that cause an allergic reaction are called allergens. Besides dust and pollen, other

common allergens include animal dander, foods, including nuts and shellfish, and certain

medicines, such as penicillin. Allergy symptoms can range from sneezing and a stuffy nose

to a life-threatening complication called anaphylactic shock. Allergy blood tests measure the

amount of IgE antibodies in the blood. A small amount of IgE antibodies is normal. A larger

amount of IgE may mean you have an allergy.