An allergy is a specific reaction to a normally harmless substance. Those who have allergies are often sensitive to more than one substance. An allergic reaction can occur in several different ways. Airborne particles such as pollen, dust and mold spores are breathed in through the nose and mouth. Insect venom is injected through stingers from bees and wasps. Foods are swallowed and ingested. Medicines that can cause allergic reactions can be either injected or ingested. Upon contact with skin, substances such as latex, nickel, cosmetics and oil found in plants such as poison ivy can also cause allergic reactions.

An estimated 50 to 60 million Americans (about one out of every five adults and children) suffer from allergies in the United States.

Allergies can be genetic. If only one parent has allergies, chances are 1 in 3 that each child will have an allergy. If both parents have allergies, it is much more likely (7 in 10) that their children will have allergies.

Allergies are responsible for 3.4 million lost U.S. work days each year, at a cost of $639 million. An estimated two million school days are lost each year due to allergies.

Consumers and employers spend as much as $2 billion per year on allergy treatment, including office visits, tests, medications and immunotherapy (allergy shots).

Allergy sufferers account for more than 8.4 million physician visits each year, and $225 million is spent on physician services annually.

More than 33 million Americans suffer from chronic sinusitis (sinus infections). These infections are more common in chronic allergy sufferers.

More than 22 million Americans have allergic rhinitis, or hay fever. It is the most frequently reported chronic condition in children, limiting activities for more than 40 percent of them.

An estimated 6 to 10 million Americans are allergic to cats.

An estimated 2 million Americans develop severe allergic reactions to insect stings.

Food allergies are believed to occur in 8 percent of children younger than 6 years old. In adults, approximately 1 to 2 percent are sensitive to foods or food additives.

There are an estimated 42,000 cases of adverse drug reactions reported annually.

More than HALF of all allergy sufferers fail to recognize their symptoms at first, falsely believing they have a cold or the flu.