How do allergy shots work? How many? How often?

December 11, 2002, updated June 12, 2003

The shots work the same whether you are allergic to dust mites or to other allergens such as pollens, mold, or animals. As controlled amounts of the items you are allergic to are injected into the tissues just under your skin, your body begins building blocking antibodies toward that substance.

The prefix "anti" means "against." Think of blocking antibodies as an army of specialized warriors fighting against the invading allergen.

If 10,000 allergic soldiers invade we may be overcome with sniffles and sneezes. Our immune systems just aren't equipped to fight such a battle. But if only 20 allergic soldiers invade (as in the controlled allergy shots) our immune system can build it's army of blocking antibodies quickly to ward off the attack.

These blocking antibodies linger around for awhile to guard the newly established war zone. But if no further invasions occur, the body begins to decrease its population of blocking antibodies. However if another invasion (allergy shot) occurs within a few days, not only do many of the original blocking antibodies remain to fight, but new blocking antibodies are developed as well.

Each allergy shot is a little stronger than the previous one. First, there's just a tiny dose of allergen (the fictional 20 allergic soldiers), then perhaps 30 more allergic soldiers will be introduced with the second shot.

More blocking antibodies are produced as increasingly larger amounts of allergen are given by injections. The goal is to eventually produce an army of blocking antibodies so great that it can easily defeat that 10,000 allergic soldier invasion.

As the allergens invade through the skin (shots) rather than the air (respiratory allergy), they sometimes seems less threatening to the body. As a result, sensitivity to the offending allergens often decreases. This means that when immunotherapy is stopped, you may no longer have an allergic response to the things which once caused allergy symptoms.

In order to accomplish this, shots must be given regularly, usually on a weekly basis at first. The extract for these shots is diluted from concentrated extracts, and the dilution is gradually increased until full concentration is reached.

Once the concentrated level is reached, this is considered the maintenance level. It usually takes anywhere from several months to well over a year to reach this level. At this point, we gradually spread shots out to every two weeks, then eventually every three to four weeks.

Occasionally a patient will begin having a lot of swelling around the site of the injection before we reach the concentrated dose. For these people we may "back off" a little and try again, but if they continue to be unable to tolerate increasing doses we stop them where they are for maintenance. Sometimes after several months of "maintenance" at a lower level, we are able to progress them on to the concentrated dose.

We advise our patients to continue the allergy injections for a total of 3-1/2 to 5 years, with 5 years being optimal for a greater chance that symptoms won't return when shots are stoped. Some patients choose to continue the immunotherapy beyond five years for even greater resistance to invading allergens.

We follow generally accepted guidelines that many other allergy clinics follow as well. But each clinic will have it's own adaptation of these guidelines. You will need to check with your allergy doctor for his exact recommendations and plan for your care.

See also:
Weekly injections: Are they necessary?

I'm taking allergy shots. When will I feel better?

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