Allergy Shots (Allergen Immunotherapy)

Content provided by the Faculty of the Harvard Medical School

What Is It?

Allergic symptoms — the familiar sneezing, runny nose, itchy eyes or asthma attacks — are caused by the body's reaction to a substance (allergen) that is inhaled, touched or eaten. You also can develop a rash from a substance you touch or get stomach upset, hives or difficulty breathing from something you eat. These allergens cause no symptoms in a non-allergic person, but in an allergic person, an immune reaction against the allergen causes symptoms. In allergy, the body responds to the allergen as it would respond to a dangerous invader, such as bacteria or a virus. The immune system recognizes the substance as foreign and activates an army of antibodies to eliminate the invader. The antibodies bind with the allergen and stimulate the release of chemicals, such as histamine, that cause allergy symptoms.

Standard treatment for mild to moderate allergies involves avoiding the allergen that causes the allergic reaction and taking over-the-counter or prescription medications. But when these options are not enough to get rid of symptoms, if allergies are severe or if you have significant side effects from taking your prescription medications, allergy shots may be recommended.

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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.

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Before allergy shots can be given, you must have tests to determine which allergens are causing your allergic reactions. These tests include skin or patch testing and a blood test called a radioallergosorbent test (RAST). The tests are not always accurate, so you can have a positive test with no allergy symptoms or a negative test and still have allergy symptoms.

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How It's Done

When you get an allergy shot, a small amount of allergen is injected under the skin, usually in the fleshy part of the upper arm. In the beginning, injections usually are given once a week, and the doses of allergen are increased gradually with each injection. The maximum dose, called a maintenance dose, is reached after four to six months. The maintenance dose is given once a week or once every two weeks. After several months, the injection schedule may be reduced to once every three or four weeks. A full course of allergy shots usually takes between three and five years.

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After each injection, you will be asked to remain in the clinic or waiting room for 20 minutes or longer so that any reactions to the injection can be recognized and treated immediately. People receiving allergy shots will be asked to keep to a strict schedule of injections, because missed injections may reduce the benefits and delay the effectiveness of treatment.

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Most people do not have any bad reactions to allergy shots. Sometimes, you may develop swelling, redness or itching at the site of the injection. These mild reactions typically are treated with antihistamines, and your doctor may decide to adjust the dose for the next injection.

On rare occasions, a more severe reaction will occur. In some sensitive people, the allergy shot can cause asthma symptoms, including difficulty breathing, wheezing or coughing. Or, an anaphylactic reaction will cause dizziness, nausea, a swelling of the throat that can prevent breathing or tightness of the chest. These reactions usually can be treated in the office, but occasionally, they may require treatment at a hospital.

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When To Call a Professional

Call your physician or allergist if you notice any redness or swelling at the site of the injection, or if you experience any coughing or wheezing after a recent injection. If you develop difficulty breathing or talking, tightness in the chest, or if your throat is closing, you or someone with you should call your local emergency number.

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Additional Info

American Academy of Allergy, Asthma and Immunology (AAAAI)
555 East Wells St.
Suite 1100
Milwaukee, WI 53202-3823
Phone: 414-272-6071

National Institute of Allergy and Infectious Diseases (NIAID)
Office of Communications and Public Liaison
6610 Rockledge Drive, MSC6612
Bethesda, MD 20892-6612
Phone: 301-496-5717
Toll-Free: 1-866-284-4107
TDD: 1-800-877-8339

Last Annual Review Date: 2008-07-10T00:00:00-06:00 Copyright: © 2010 by Harvard University. All rights reserved. Used with permission of StayWell.