In the US, one in ten people suffer from some form of allergy. Allergic reactions range from life threatening as in the case of allergies to bee stings or penicillin to responses as mild as sneezing when you sniff a flower to which you are sensitive. Regardless of the severity, the underlying cause of most allergic reactions is the same. An allergic reaction is triggered when the body's immune system over-reacts to the presence of something that is not usually found in the body. The allergen can get there by being eaten or inhaled, or by injection as may occur with an insect sting.
Allergic reactions occur most commonly to pollen grains, dust, molds and foods.
Allergic reactions can also occur to animal proteins such as those found on hair, fur, or dander, and to topical agents such as the oils found on poison ivy leaves. Once on the mast cell surface, allergen-specific IgE can remain for weeks or even months, always ready to bind to the original allergen. The next time the allergen enters the body, the allergic cascade begins and eventually results in the release of histamines from the mast cell. As annoying as the symptoms of alergy are, they do serve a purpose - they are an attempt by the body to wash away the offending allergen. Pollen is the No. 1 allergen, or troublemaker maker for people with allergies.