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Allergy Shots (Allergen Immunotherapy)

Medically reviewed by Last updated on Dec 9, 2022.

What are allergy shots?

Harvard Health Publishing

Allergy shots are a treatment that can help to prevent or minimize allergic reactions. They are personalized to each patient—the shots are only useful when specific allergy triggers have been identified. Allergy shots are received on a schedule, over a period of several years.

What allergy shots are used for

Common allergic symptoms are sneezing, runny nose, itchy eyes or asthma attacks. Allergy symptoms are caused by your body's reaction to a substance (allergen) that is inhaled, touched or eaten. Allergens cause no symptoms in a non-allergic person, but in an allergic person who is sensitized to that antigen, an immune reaction against the allergen causes symptoms. 

In allergic reactions, the body responds to the allergen in the same way it would respond to fight off infection by a parasite. 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 then trigger immune system cells to release chemicals, such as histamine. This release of histamine is what causes most allergy symptoms.

Allergy Shots (Allergen Immunotherapy)

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 typical course is at least three 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 treated with allergy shots. The risk for having an anaphylaxis reaction is too high. However, some children with food allergies have successfully been treated with a treatment that is similar to allergy shots—oral immunotherapy. Oral immunotherapy is given by mouth, not as a shot. It is being used more frequently, but  it is still considered experimental.  

Avoidance of foods to which you are allergic currently the best strategy for preventing food allergy reactions. 

Preparing allergy shots

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

How allergy shots are 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 are typically given once a week. After that, 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.

Following-up allergy shots

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.

Risks of allergy shots

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.

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.

Additional Info

American Academy of Allergy, Asthma and Immunology (AAAAI) /home

National Institute of Allergy and Infectious Diseases (NIAID)


Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.