Immunotherapy: How Allergy Shots Work

When medications fail to adequately control allergy symptoms and avoiding the trigger is not easy or possible, an allergist may recommend immunotherapy, or allergy shots. This treatment consists of a series of injections containing small amounts of the substances to which a person is allergic.

After a course of allergy shots, patients have fewer allergy symptoms. Allergy shots can be given for allergic rhino-conjunctivitis (nose and eyes), allergic asthma, and insect sting allergies.

This article explains how allergy shots work, how they're given, and how long they last. It also describes the risks of getting the shots and how to decide if you're a good candidate for them.

Overview

Allergy shots have been around for nearly 100 years and are approved by the U.S. Food and Drug Administration. Numerous well-designed medical studies show the efficacy of allergy shots. They do not contain steroids, which can have adverse long-term side effects.

Unlike allergy medicines, which act only to “cover up” allergic symptoms or prevent them temporarily, allergy shots address the underlying problem of allergies. This occurs because the body treats the injection much like a vaccine, resulting in the production of infection-fighting antibodies against pollen, dust, mold, or pet dander.

The body then stops producing as many allergic antibodies against the triggers and, therefore, won’t have as much, or any, allergic response when exposed to the allergens. These changes can last for many years, even after the allergy shots are no longer taken. Some studies show that allergy shots can also prevent people from developing new allergies and reduce the risk of developing asthma in children with nasal allergies.

Method and Dosage

The method of immunotherapy consists of starting at a small dose, which will not cause an allergic reaction, and slowly advancing the dosage until the person becomes tolerant to large amounts of the extract. These injections are initially given once or twice a week until a maintenance, or constant dose, is achieved. This usually takes between three and six months.

After this time, symptoms generally start to improve. Thereafter, the injections are given every two to four weeks.

Duration of Treatment

Therapy is continued for three to five years total, after which the patient continues to benefit for another five to 10 years or longer, even after the shots are stopped. If the shots are stopped prior to a total of three years, the allergic symptoms typically return more quickly.

Risks

The risks of immunotherapy consist of the possibility of experiencing an allergic reaction to the allergy shot. Most allergic reactions involve mild to moderate swelling and itching at the site of the injection.

These reactions occur frequently, but rarely require any change in treatment. A large swelling may require an adjustment to the immunotherapy dosage or a change in the frequency and number of shots.

Less commonly, patients experience whole-body allergic reactions, sometimes called “anaphylaxis.” Most of these reactions are mild and consist of itching of the skin, hives, or a runny nose. Others are more severe and can present as cough, chest tightness, wheezing, throat tightness, or shock. Rarely are these reactions life-threatening.

For this reason, it's normally required that patients remain in the healthcare provider's office for 20 to 30 minutes after the injection since most reactions occur during this time. These reactions are typically easily reversed with medicines, such as injectable epinephrine and antihistamines.

Eligibility

Deciding whether you are a good candidate for immunotherapy is a question that only you and your healthcare provider can answer. That said, there are several reasons to consider allergy shots:

• Your medication isn't working: Many people see an allergist because they continue having symptoms despite having tried numerous allergy medications. Sometimes, allergy shots are the only therapy left for these patients.
• Taking medication doesn't suit you: Some people experience severe side effects from medication or don’t like taking medication on a daily basis. The idea of a once-a-month shot is a better option for them.
• Your medication is getting too pricey: Medication can be expensive, and the cost tends to consistently increase, not decrease. Since allergy symptoms typically return soon after medications are stopped, patients may require medication for many years. Allergy shots can alleviate much of the need for medication and can be a significant money-saver in the long run.
• You want to feel better: Allergy shots are not a 100% curative option, but they can drastically improve symptoms (upwards of 80% for outdoor pollen allergies). Meanwhile, some patients enjoy a complete remission of their symptoms.

Summary

Allergy shots address the underlying problem that triggers an allergy because the body treats the injection much like a vaccine. This results in the production of infection-fighting antibodies. Over time, the body then stops producing as many allergic antibodies against the trigger and, therefore, won’t have as much, or any, allergic response when exposed to the allergens. These changes can last for many years, even after the allergy shots are no longer taken. Some studies show that allergy shots can also prevent people from developing new allergies.

A Word From Verywell

If you're considering immunotherapy, it may be helpful to think about the transition taking place in two phases. The "buildup phase" takes about three to six months, during which time the allergen dose gradually gets stronger. The "maintenance phase" continues for three to five years or longer, during which time you will need about one shot a month.