Each injection contains a small amount of the allergens you react to. By exposing yourself to these small doses, you develop a tolerance to the allergen. In other words, your body will stop reacting to the allergen as if it were a poison. It will no longer produce the antibodies when it is exposed to the allergens, and you will no longer experience hay fever symptoms. The full course of allergy injections must be continued for several years to be completely effective.
Research is now under way on a nasal spray that works in a way similar to allergy injections.
If this treatment turns out to be safe and effective, it will have several advantages over the injections. The first, of course, is convenience. More important, however, the nasal spray will affect only those parts of your body that develop the allergic symptoms. However, there are many other substances floating in the air that can lead to similar allergic reactions. These include molds, animal dander, and dust.