Brent Stewart, age 9, of Hennessey, Okla., for his question:

HOW DOES AN ALLERGY DEVELOP?

An allergy is a body reaction that happens in people who are sensitive to certain substances. About 15 percent of the people in the United States and Canada have an allergy that requires repeated medical treatment.

A substance that causes an allergy is called an allergen. An allergen is capable of stimulating the body to produce proteins called antibodies. The allergens and the antibodies together can release certain substances from the body cells into the blood and other body fluids. These substances are called H substances and they bring about reactions in other cells or tissues. Many different H substances can cause allergic reactions in man and animals.

There is no complete cure for allergy. A person may be able to avoid the symptoms of a particular allergy by avoiding the allergen that causes it.