Allergy Immunotherapy Overview

This article is part of our Allergy Treatment resource center, covering all aspects of allergy treatment diagnosis, treatment, and management.

Unlike antihistamines and nasal corticosteroids, which manage symptoms without changing the underlying immune response, allergen immunotherapy (AIT) works by retraining the immune system. It is part of the broader set of allergy treatment options that an allergist may consider for appropriate patients.

How Immunotherapy Changes the Immune Response

In allergic individuals, the immune system produces IgE antibodies against harmless substances such as pollen, dust mite proteins, and animal dander. When exposed to these substances, mast cells and basophils release histamine and other inflammatory chemicals, producing symptoms. Allergen immunotherapy works by introducing the allergen in controlled, gradually increasing doses. Over time, this shifts the immune response: the body increases production of IgG4 "blocking" antibodies, promotes regulatory T-cell activity, and reduces mast-cell sensitivity to the allergen. The result is reduced reactivity to the allergen both during and after the treatment period.

Forms of Allergen Immunotherapy

Subcutaneous Immunotherapy (Allergy Shots)

Traditional allergy shots (SCIT) have been used for over a century and have the most extensive evidence base. Injections are given in an allergist's office or supervised clinical setting. A build-up phase begins with low-dose injections — often once or twice weekly — gradually increasing to the target maintenance dose over several months. The maintenance phase then involves injections at longer intervals (typically every 2 to 4 weeks). Subcutaneous immunotherapy is available for a wide range of allergens including pollen, dust mites, animal dander, mold, and insect venom. Because of the small risk of systemic reactions, patients are asked to wait in the clinic for 20 to 30 minutes after each injection.

Sublingual Immunotherapy (Tablets and Drops)

Sublingual immunotherapy (SLIT) delivers allergen extracts under the tongue, where specialized immune cells in the oral mucosa promote tolerance. FDA-approved sublingual tablet products are available for specific allergens including grass pollen, ragweed pollen, and house dust mites. These tablets are typically taken daily and, after the initial supervised dose, can be taken at home — a significant convenience advantage over shots. See our full sublingual immunotherapy guide for more detail on approved products and how they compare to shots.

Allergy drops (liquid SLIT) are also used by some allergists in the United States. Unlike the approved tablets, compounded drops are not currently FDA-approved as allergen immunotherapy products, which has regulatory and insurance implications that differ from approved tablet formulations. Your allergist can explain the distinction for your situation.

Oral Immunotherapy for Food Allergy

Oral immunotherapy (OIT) involves consuming small, gradually increasing amounts of a food allergen under close medical supervision to raise the reaction threshold. FDA-approved peanut OIT (Palforzia) is available for eligible patients at participating allergy centers. See our OIT guide for detailed information on protocols, eligibility, and what to expect during treatment.

Build-Up and Maintenance Phases

Most immunotherapy programs involve two phases. During the build-up phase, allergen doses increase gradually to allow the immune system to adapt without triggering a significant reaction. Depending on the schedule and the allergen, this phase may take several months. The maintenance phase begins when the target dose is reached and focuses on sustaining the immune tolerance that has been established. Maintenance doses are typically given less frequently than build-up doses. Consistent adherence throughout both phases is important for achieving optimal benefit.

Conditions Commonly Treated

Immunotherapy is most commonly used for:

• Allergic rhinitis (hay fever) from pollen, dust mites, mold, or animal dander
• Allergic asthma where specific triggers have been identified by testing
• Insect venom allergy (bee, wasp, yellow jacket, hornet) — venom immunotherapy significantly reduces risk of severe reactions
• Food allergy (peanut OIT; investigational programs for other foods)

Accurate allergen identification through allergy testing is a prerequisite before beginning immunotherapy.

Who May Be a Candidate

Immunotherapy is typically considered when symptoms are not adequately controlled by medications and avoidance, or when a patient prefers a treatment approach aimed at long-term tolerance rather than ongoing medication use. It may also be appropriate for patients with insect venom allergy who are at risk for anaphylaxis, or for patients whose allergy medications are causing significant side effects or interfering with daily function. Certain conditions may affect candidacy — including uncontrolled asthma, certain cardiovascular conditions, and use of some medications. An allergist evaluation is needed to determine whether immunotherapy is appropriate and which form is best suited to the individual.

Expected Timeline and Effectiveness

Immunotherapy is a long-term commitment. Gradual improvement typically occurs over months, with more substantial benefit accruing over 1 to 3 years of treatment. Most clinical guidelines recommend continuing treatment for 3 to 5 years to achieve lasting benefits that persist after immunotherapy ends. Some patients experience significant ongoing relief for several years after completing treatment; others may need retreatment if symptoms return.

Effectiveness varies by allergen, patient factors, and adherence. An allergist will monitor your response throughout treatment and can advise whether continued therapy is likely to be beneficial.

Safety and Reactions

Local reactions at the injection site are common with SCIT and generally mild. Systemic reactions — such as sneezing, urticaria, or airway symptoms — are less common and are more likely during the build-up phase or if a dose is given when the patient is acutely ill or has recently exercised. Serious anaphylactic reactions are rare but possible, which is why SCIT injections must be given in a clinic equipped with epinephrine and emergency equipment, with mandatory post-injection observation. Sublingual immunotherapy carries a lower risk of systemic reactions but can cause local oral symptoms (itching, tingling).