According to the leading experts in allergy, an allergic reaction begins in the immune system. Our immune system protects us from invading organisms that can cause illness. If you have an allergy, your immune system mistakes an otherwise harmless substance as an invader. This substance is called an allergen. The immune system overreacts to the allergen by producing Immunoglobulin E (IgE) antibodies. These antibodies travel to cells that release histamine and other chemicals, causing an allergic reaction.
An allergic reaction typically triggers symptoms in the nose, lungs, throat, sinuses, ears, lining of the stomach or on the skin. For some people, allergies can also trigger symptoms of asthma. In the most serious cases, a life-threatening reaction called anaphylaxis (an-a-fi-LAK-sis) can occur.
A number of different allergens are responsible for allergic reactions. The most common include:
• Insect stings
• Animal dander
via Allergies | AAAAI.