An allergist is the only person who is qualified to prescribe and supervise this form of treatment. In fact, desensitisation therapy requires a deep understanding of allergic disease. The protocol includes different phases spread out over a long period (three to five years).

Two routes can be used to administer the therapeutic allergen:

•  Subcutaneous administration:
  The allergen is subcutaneously (under the skin) injected in the upper arm between the elbow and the shoulder. The injections are painless and must be given by the allergist (at least in the early stages of the procedure), and are followed by a 30-minute monitoring period in the doctor's office or clinic.

•  Sublingual administration:
  This route only came into widespread use recently but gives similar results to subcutaneous injection. Administration takes place at home, in the morning before breakfast, by applying drops of the allergen solution directly under the tongue and then leaving them there for 2 minutes. It is necessary to show strict self-discipline in order to promote optimal efficacy of the treatment.

All desensitisation protocols are tailored to the patient's specific case and involved 2 successive phases:

• The first phase, referred to as the "initial treatment" phase, has the purpose of stepping up the treatment's strength. Starting at a very low dose of the allergen involved, the allergist increase the dose of the product administered over the course of the first few weeks of treatment until the highest well-tolerated dose is reached. Depending on the route of administration (subcutaneous injection or sublingual administration) being used and the individual's sensitivity, this initial phase may last anywhere from 11 days to 14 weeks, or even one day.

• The second phase, referred to as the"maintenance phase", can then begin. The maximum dose tolerated by the patient at the end of the initial phase is then given at regular intervals (depending on the route of administration and the individual's sensitivity) for a period ranging from 3 to 5 years or several pollen seasons.