What Causes the Sneezing, Itchy Eyes and Other Symptoms?
When a sensitive person inhales an allergen (allergy-causing substance)
like ragweed pollen, the body's immune system reacts abnormally with
the allergen. The allergen binds to allergic antibodies (immunoglobulin
E) that are attached to cells that produce histamine and other chemicals.
The pollen "triggers" these cells in the nasal membranes, causing
them to release histamine and the other chemicals. Histamine dilates the
small blood vessels of the nose and fluids leak out into the surrounding
tissues, causing runny noses, watery eyes, itching, swelling and other
Antibodies circulate in the blood stream, but localize in the tissues of
the nose and in the skin. This makes it possible to show the presence
of these antibodies by skin testing, or less commonly, by a special blood
test. A positive skin test mirrors the type of reaction going on in the nose.