treatment that attempts to eliminate allergic reactions, as of hay fever or bronchial asthma, by a series of injections in graded strengths of the substance to which the person is sensitive (e.g., pollen, house dust). Extracts of the material to be injected are purified and put into an alkaline buffer solution, to which epinephrine (epinephrine and norepinephrine) (adrenaline) is often added to minimize local inflammatory reactions. The first injections contain little antigen, but, as desensitization progresses, more and more is added. A three-month program of injections often suffices for hay-fever (hay fever) sufferers, but asthmatics (asthma) may require a longer program.

Desensitization is successful in about 80 percent of hay-fever sufferers and up to 90 percent of asthmatics; treatment is more effective in persons with a few, well-defined allergies than in those allergic to many substances. The success of desensitization is attributed to special antibodies, called blocking antibodies, that appear in the serum after treatment and combine preferentially with allergen. This prevents the reaction of allergen with allergic antibodies in the skin and precludes an allergic reaction. Desensitization can also be required when a penicillin-sensitive person contracts a disease such as bacterial endocarditis, which is best treated with penicillin. See also allergy; anaphylaxis; antibody; antigen.