Breath of Fresh Air: Feature Articles

Allergy shots (properly called allergy desensitization injections or allergen immunotherapy) have been used in the treatment of asthma for more than 80 years. The idea behind this practice is straightforward: if one exposes the immune system to very minute quantities of a substance to which it makes allergic reactions, the immune system may gradually grow tolerant to that substance and stop making harmful reactions to it. For example, if one repeatedly injects under the skin small amounts of the allergenic substance in cat dander, one might gradually lose one's sensitivity to cats.

The purpose of allergy shots: by repeated exposure, make the immune system tolerant of specific allergens.

Although the basic principle is relatively simple, its practice is complicated. For one thing, one has to be sure that one is allergic to cats (or mold or dust mites or ragweed) and that this is the major culprit causing asthma symptoms. It would do no good becoming desensitized to cats while continuing to smoke cigarettes, live in a dusty home, and keep parrots. In addition, one has to take care not to give too much cat antigen as part of the allergy shots and trigger an asthmatic reaction. Because the antigen is injected under the skin, one might cause a reaction throughout the entire body, with low blood pressure, itching, and wheezing — a potentially life-threatening reaction called anaphylaxis (pronounced: anna-phil-LAX-is). With each injection comes some risk, although small, of a harmful allergic reaction to the injection.

Allergy shots carry some risk.

Finally, one depends on the ability of medical companies to isolate and purify the chemical component of cat dander (or other allergens) to which one is allergic. For some allergies these substances are well characterized and purified; for others this is not yet the case. Thus, there may be variation between one lot of allergen and another and between one allergist's preparations and another.

What about the benefits from allergy shots? The potential promise is that allergy shots might lead to fewer asthmatic symptoms, reduce the need for daily medications, and correct the basic allergic mechanisms in the body. Evidence supports the use of allergy shots for severe hay fever and for severe bee or wasp sting reactions, but in asthma the benefits are less clear. Here is where the controversy enters. Some studies have shown a benefit from allergy shots in asthma, others have not. Some doctors believe that the potential benefits from allergy shots justify the risks — and costs and inconvenience of weekly doctor's visits for the initial 3-6 months. Other doctors believe that routine medical treatments for asthma with tablets and/or inhalers are safer and more effective than allergy shots, which may be of limited benefit.

How effective are allergy shots for asthma?

All of us agree that allergy can be an important cause of asthma symptoms and that avoiding exposure to allergens — in the home and at work — is an important part of the treatment for asthma. If, in addition, one is considering allergy shots, one should check the following:

• Can it be shown by allergy skin tests that I am allergic to one or more specific allergens?

• Do my asthma symptoms come on when I am exposed to those allergens?

• Have I already taken measures to minimize exposure to those allergens at home or at work?

• Is my asthma still troublesome despite conventional asthma treatments?

• Are well-standardized allergens available for desensitization treatments?

• Is my asthma sufficiently severe to justify the cost, inconvenience, and risk of allergy shots?