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Harvard Medical School

Allergy Shots (Allergen Immunotherapy)

What It's Used For

Allergy shots, also known as allergen immunotherapy, is a way of desensitizing the body so that it stops reacting strongly to certain allergens. Tiny amounts of the offending substance are injected under the skin to stimulate the immune system a little each time. Gradually, over weeks and months, the amount of allergen is increased. It's not completely clear how allergy shots work, but it is believed the treatment stimulates a different type of immune reaction against the allergen which is less bothersome than a traditional allergic response. Allergy shots do not provide short-term relief, but they can be a good long-term solution when they work well. Many people have reduced allergy symptoms for many years after going through a full course (three to five years) of allergy shots. It can take about six months to a year for symptoms to start to subside. For people who respond to the treatment, allergy shots can significantly decrease the severity of symptoms and decrease how often the symptoms occur. However, for some people, there may be no or little effect even after a year.

Allergy shots usually are recommended for people with severe allergy symptoms who do not respond to usual medications or have significant side effects from their medications. Other candidates include those who find their lives disrupted by allergies, or for whom allergies might become life threatening, such as people who develop asthma attacks or a severe allergic reaction called anaphylaxis. It also 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.