Allergen immunotherapy (allergy shots or vaccine) involves injecting small amounts of inhaled allergens or venoms. Allergy testing and careful history determine what each patient’s injection contains. 

Allergy shots work by vaccinating a person against specific inhaled allergens to which that person is allergic. Venom therapy for stinging insect allergy works in the same way. 

When a person is exposed to allergens by an injection (allergy shot), the body is tricked into responding to these specific allergens in a different way. Gradually increasing the amount and strength of allergen in the shots suppresses production of the allergy antibody, referred to as IgE. Allergy shots increase the production of blocking antibody (IgG) which helps prevent the allergen from attaching to mast cells. Mast cells explode and release the chemical mediators, such as histamine, that cause inflammation and allergy symptoms.