What is desensitization?

A behavioral method: Desenitization actually is used in a variety of settings. In mental health, it refers to the graded exposure to a feared activity or object, e.g., snakes or spiders. Usually, relaxation techniques are part of the process. Then, starting perhaps with just visualizing the feared object, the person gradually increases exposure until it becomes "routine." well studied and can be highly effective.

For allergy..: Desensitization is the process of exposing the immune system to gradually increasing doses of a substance for the purpose of creating a degree of tolerance. This can be done with allergy shots for patients with allergic rhinitis, oral desensitization to a medication such as an antibiotic, or intravenously for a severely ill patient that requires a medication they are allergic to.