Allergic diseases constitute a health problem worldwide. More than just a treatment option, the classical desensitization (SIT--Specific immunotherapy) by subcutaneous injection has profiled over time as a unique approach, able to attenuate the immune response to allergic stimuli proved. For a long time conservative, desensitization has now progressed in the knowledge of allergens, in the understanding of the mechanisms involved in immune response and in production techniques. From recombinants to alternative routes of allergen delivery, this article gives an overview of new perspectives and assesses SIT in order to provide guidance to the general physician before choosing to initiate such treatment or not in patients with respiratory allergy.