Immunotherapy does not treat symptoms; it treats the immune system, the source of all allergic reactions. Although the exact details of how allergy shots work is unknown, we do know the general way they affect the immune system.

An allergic reaction occurs when the body is exposed to an external substance (the antigen) that the immune system interprets as a foreign invader. In allergic individuals, the immune system then makes an unusual (allergic) response that harms the body.

• The white blood cells produce an antibody to the antigen called immunoglobulin E, or IgE. This is called sensitization.

• When the antibody comes in contact with the antigen, it promotes release of certain chemicals called mediators into affected tissues. Histamine is an example of a mediator.

• It is the effects of mediators on organs and cells that cause the symptoms of allergic reactions.

• This overreaction to a harmless substance is often called a hypersensitivity reaction.

Allergy shots desensitize you by turning down this immune response to the antigen. As a result of immunotherapy, the white blood cells no longer respond as strongly to the antigen, and less production of the immunoglobulin E antibody to this antigen occurs. So, when you are exposed to this antigen, less severe allergic reactions occur in affected areas like the eyes, nasal mucosal surfaces, and the bronchial airways.