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Medical Content Created by the Faculty of the
Harvard Medical School

Allergy Shots (Allergen Immunotherapy)

What It's Used For

Allergy shots, also known as allergen immunotherapy, cause the body to stop generating symptoms after exposure to certain allergens. Tiny amounts of the offending substance are injected under the skin with each shot. The shots stimulate the immune system just a little each time. Gradually, over weeks and months, the amount of allergen is increased.

This very constant, low-level exposure stimulates a different type of immune reaction against the allergen. This new pattern of immune reaction substitutes for and is less bothersome than a traditional allergic response.

Allergy shots can be a good long-term solution when they work well. For people who respond to the treatment, allergy shots can make allergy symptoms less severe and can cause them to occur less often.

Many people benefit from allergy shots for many years after going through a full course of shots. A full course is three to five years. It can take about six months to a year for symptoms to start to subside. For some people, there may be no or little effect even after a year of treatment—in this case, it is not worth continuing the treatment.

Allergy shots are recommended for people with severe allergy symptoms who do not respond to usual medications. They are useful for people who have significant side effects from their medications. They can also be useful for people who find their lives disrupted by allergies, or people for whom allergies might become life threatening, such as people who develop asthma attacks or a severe allergic reaction called anaphylaxis. Allergy shots can be used to reduce the severity of reactions to insect stings.

Not all allergies can be treated with allergy shots. Food allergies are not usually treated with allergy shots, because the allergic reaction from food allergies (anaphylaxis) makes the injections high risk, even though very small quantities of antigen are used in the shot. Avoidance of foods to which you are allergic is a better strategy.