allergy-asthma
How Do Allergy Shots Work? Immunotherapy Explained
Allergy shots (subcutaneous allergen immunotherapy) work by gradually introducing increasing doses of your specific allergens, slowly retraining the immune system to tolerate rather than overreact. The build-up phase involves weekly injections for about a year; the maintenance phase continues monthly for three to five years, with meaningful benefit typically starting within the first year.
What is happening inside your immune system?
In allergic disease, the immune system has produced IgE antibodies against a harmless substance (pollen, dust mites, pet dander). When you are re-exposed, those IgE antibodies trigger mast cells to release histamine and other inflammatory mediators, causing your symptoms.
Allergen immunotherapy works by repeatedly exposing the immune system to small, gradually increasing doses of the offending allergen. Over time this shifts the immune response — reducing IgE production, increasing blocking antibodies (IgG4), and promoting regulatory T-cell activity that dampens the allergic reaction 1Ref 1Gurgel RK, Baroody FM, Damask CC, Mims JW, Ishman SL, Baker DP Jr, et al. (2024).Clinical Practice Guideline: Immunotherapy for Inhalant Allergy.Mechanism of allergen immunotherapy, build-up and maintenance phases, candidate selection, SCIT vs SLIT evidence, and long-term benefit after completing treatment2Ref 2Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011).Allergen immunotherapy: a practice parameter third update.Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit. The goal is to move from an overreactive immune response toward tolerance.
This is distinct from antihistamines and corticosteroids, which treat symptoms after the reaction has begun. Immunotherapy works upstream at the level of immune memory.
What is the build-up phase?
The build-up phase typically involves weekly injections of gradually increasing allergen doses, usually over six to twelve months 2Ref 2Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011).Allergen immunotherapy: a practice parameter third update.Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit. Each injection contains a slightly higher concentration than the previous one. The build-up phase is the period of greatest immune reprogramming, but also the period when reactions to the injections are most likely — for this reason, patients remain in the clinic for 20–30 minutes after each injection for observation 3Ref 3Bernstein DI, Epstein TE (2020).Safety of allergen immunotherapy in North America from 2008-2017: Lessons learned from the ACAAI/AAAAI National Surveillance Study.30-minute post-injection observation standard; systemic and anaphylactic reaction rates; safety outcomes across 10 years of North American practice.
Accelerated schedules (cluster and rush immunotherapy) compress the build-up period to weeks, but carry a higher reaction risk and are not appropriate for everyone 2Ref 2Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011).Allergen immunotherapy: a practice parameter third update.Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit.
What is the maintenance phase?
Once the target maintenance dose is reached, injections become less frequent, typically monthly 2Ref 2Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011).Allergen immunotherapy: a practice parameter third update.Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit. Most people continue maintenance injections for three to five years.
Symptom improvement usually begins within the first six to twelve months and continues to increase through maintenance treatment. After completing a full course, many people experience sustained benefit — reduced sensitivity — even after stopping shots 1Ref 1Gurgel RK, Baroody FM, Damask CC, Mims JW, Ishman SL, Baker DP Jr, et al. (2024).Clinical Practice Guideline: Immunotherapy for Inhalant Allergy.Mechanism of allergen immunotherapy, build-up and maintenance phases, candidate selection, SCIT vs SLIT evidence, and long-term benefit after completing treatment2Ref 2Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011).Allergen immunotherapy: a practice parameter third update.Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit.
Which allergens can be treated?
Allergen immunotherapy is most established and most effective for 1Ref 1Gurgel RK, Baroody FM, Damask CC, Mims JW, Ishman SL, Baker DP Jr, et al. (2024).Clinical Practice Guideline: Immunotherapy for Inhalant Allergy.Mechanism of allergen immunotherapy, build-up and maintenance phases, candidate selection, SCIT vs SLIT evidence, and long-term benefit after completing treatment2Ref 2Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011).Allergen immunotherapy: a practice parameter third update.Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit: - Airborne allergens: tree, grass, and weed pollens; dust mites; cat and dog dander; mold - Insect venom: bee, wasp, yellow jacket, and fire ant stings (venom immunotherapy is highly effective at preventing life-threatening reactions) - Some occupational allergens
Food allergy immunotherapy (oral immunotherapy, or OIT) is a distinct and actively evolving area, delivered differently from shot-based SCIT for inhalant allergens.
Who is a good candidate for allergy shots?
Allergy shots are a reasonable consideration when 1Ref 1Gurgel RK, Baroody FM, Damask CC, Mims JW, Ishman SL, Baker DP Jr, et al. (2024).Clinical Practice Guideline: Immunotherapy for Inhalant Allergy.Mechanism of allergen immunotherapy, build-up and maintenance phases, candidate selection, SCIT vs SLIT evidence, and long-term benefit after completing treatment2Ref 2Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011).Allergen immunotherapy: a practice parameter third update.Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit: - Allergic rhinitis, allergic asthma, or allergic conjunctivitis symptoms are not adequately controlled by medications - Medications are effective but you prefer to address the underlying cause - Medications cause side effects that limit their use - You are allergic to substances that are difficult to avoid (dust mites, pollen) - You have had a serious reaction to an insect sting
Shots are typically not started in pregnancy, in very young children (under about 5 years for most protocols), or in people with certain cardiac or pulmonary conditions that would make treating a systemic reaction difficult 2Ref 2Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011).Allergen immunotherapy: a practice parameter third update.Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit. Uncontrolled asthma is considered a contraindication 3Ref 3Bernstein DI, Epstein TE (2020).Safety of allergen immunotherapy in North America from 2008-2017: Lessons learned from the ACAAI/AAAAI National Surveillance Study.30-minute post-injection observation standard; systemic and anaphylactic reaction rates; safety outcomes across 10 years of North American practice.
What about sublingual immunotherapy (allergy drops or tablets)?
Sublingual immunotherapy (SLIT) — placing allergen extract under the tongue — is an alternative delivery method 1Ref 1Gurgel RK, Baroody FM, Damask CC, Mims JW, Ishman SL, Baker DP Jr, et al. (2024).Clinical Practice Guideline: Immunotherapy for Inhalant Allergy.Mechanism of allergen immunotherapy, build-up and maintenance phases, candidate selection, SCIT vs SLIT evidence, and long-term benefit after completing treatment. FDA-approved sublingual tablets are available for specific grass pollens, ragweed, and dust mites for allergic rhinitis. Sublingual drops are used in some practices, though drop formulations are not FDA-approved in the US and represent off-label use.
SLIT is generally considered safe enough to administer at home after the first dose is given in a clinic, making it more convenient than shots. The evidence for FDA-approved sublingual tablets for specific allergens is solid; evidence for off-label drop formulations is more variable 1Ref 1Gurgel RK, Baroody FM, Damask CC, Mims JW, Ishman SL, Baker DP Jr, et al. (2024).Clinical Practice Guideline: Immunotherapy for Inhalant Allergy.Mechanism of allergen immunotherapy, build-up and maintenance phases, candidate selection, SCIT vs SLIT evidence, and long-term benefit after completing treatment.
How do I get allergy shots?
Allergy shots are prescribed and administered by allergist-immunologists. The process begins with allergy testing to confirm which allergens you are sensitized to, followed by preparation of a customized extract. Gale can help you prepare for an allergist referral and discuss what to expect at that first appointment.
Common questions
How soon will I feel better after starting allergy shots?
Meaningful symptom reduction often begins within the first six to twelve months of the build-up phase. Benefit typically increases over the course of maintenance treatment. It is rare to notice dramatic improvement after only a few weeks.
Do allergy shots work forever, or do symptoms come back?
Many people maintain significant benefit for years after completing a full three-to-five year maintenance course. Some people require a second course if sensitivity returns. Venom immunotherapy for insect allergy may be recommended indefinitely for those at highest risk of severe reactions.
What happens if I miss a shot appointment?
Missing doses — particularly during the build-up phase — may require restarting at a lower dose to maintain safety. Your allergist will have a protocol for managing missed appointments. Consistent attendance is important for the immunotherapy to work as intended.
Are allergy shots covered by insurance?
In the US, allergy shots are commonly covered by insurance when prescribed by a board-certified allergist and when an allergic diagnosis has been established by testing. Coverage specifics vary by plan — check with your insurer before beginning.
Safety notes for allergen immunotherapy
- —Hives, itching, or swelling away from the injection site during or after a shot
- —Chest tightness, wheezing, or shortness of breath after an injection
- —Dizziness, lightheadedness, or feeling faint after an injection
Systemic reactions to allergy shots can be serious. If you experience throat tightening, difficulty breathing, or widespread hives after leaving the clinic, call 911 immediately. Carry your epinephrine auto-injector if prescribed.
This article provides general educational information about allergen immunotherapy. Whether allergy shots are appropriate for your situation requires evaluation by a board-certified allergist-immunologist.
References
- 1.Gurgel RK, Baroody FM, Damask CC, Mims JW, Ishman SL, Baker DP Jr, et al. (2024). Clinical Practice Guideline: Immunotherapy for Inhalant Allergy. Otolaryngology–Head and Neck Surgery. doi:10.1002/ohn.648 ✓Mechanism of allergen immunotherapy, build-up and maintenance phases, candidate selection, SCIT vs SLIT evidence, and long-term benefit after completing treatment
- 2.Cox L, Nelson H, Lockey R, Calabria C, Chacko T, Finegold I, et al. (2011). Allergen immunotherapy: a practice parameter third update. Journal of Allergy and Clinical Immunology. doi:10.1016/j.jaci.2010.09.034 ✓Build-up and maintenance phase dosing, candidate selection criteria, contraindications including pregnancy and severe asthma, and long-term post-treatment benefit
- 3.Bernstein DI, Epstein TE (2020). Safety of allergen immunotherapy in North America from 2008-2017: Lessons learned from the ACAAI/AAAAI National Surveillance Study. Allergy, Asthma and Proceedings. doi:10.2500/aap.2020.41.200001 ✓30-minute post-injection observation standard; systemic and anaphylactic reaction rates; safety outcomes across 10 years of North American practice
3 sources, numbered by first appearance. General health information, not medical advice — synthetic demonstration content.