So the theory behind allergy desensitization shots is this:
Inject tiny amounts of the substance you are allergic to, for the purpose of "retraining" the immune system to "accept" the allergen as "ok" and not harmful. This injection of minute amounts of the substance causes the creation of IgG antibodies to the substance, which are not believed to be involved in allergic reactions by most allergists. And it is known that IgG antibodies compete with IgE antibodies for mast cell receptor sites. So if more IgG than IgE antibodies to something are floating around in the blood, then it is more likely the IgG antibodies will stick to the mast cells and thus will block the IgE antibodies from attaching to the mast cells and triggering an allergic reaction. That's the "textbook" allergy theory behind allergy desensitization shots.
In general, it works pretty well for most people, with about
80% (or more) seeing positive results from the desensitization shots. Positive results = reduction in symptoms, or complete resolution of symptoms upon exposure to the substance(s) to which the person is allergic.
Also, usually the person is advised to take antihistamines (H1 blockers such as Claritin, etc., and also sometimes H2 blockers like Tagamet or Pepcid) prior to every allergy shot to help reduce reactivity to the small amount of substance that is injected.
My Brother has been getting allergy shots for a couple of years now and has found them to be very helpful. He used to abhor doing anything outside, and his nose used to be constantly stuffy & runny, etc. Now, he goes hiking almost every weekend no matter how heavy the pollen is outside, and gets only very mild allergy symptoms. So he has seen great results from the allergy shots.
I hope this helps...take care,