It works like a vaccine.  You are injected with gradually increasing amounts of the allergen which causes your body to develop an immunity or tolerance to it.  It can lead to decreased, minimal, or no allergy symptoms when you are exposed to the allergens.  There are two phases to immunotherapy:

 

Build-up phase.  Generally, during this phase, you will receive injections one to two times per week with increasing amounts of allergen.  This phase generally ranges from three to six months.

 

Maintenance phase.  When your effective therapeutic dose is reached, the maintenance phase begins.  During this phase, there will be longer periods of time between immunotherapy treatments.  The intervals between injections generally ranges from one every two to four weeks.  Your physician will decide what range is best for you.