Allergy Shots (Immunotherapy): How They Work and What to Expect

What you need to know

• Allergy shots are a form of allergen immunotherapy — they aim to reduce your underlying sensitivity, not just relieve symptoms day to day.
• They're used for allergic rhinitis and conjunctivitis (nose and eye allergies), allergic asthma, and severe insect-sting allergy, targeting allergens like pollen, dust mites, mold, and animal dander.
• The build-up phase involves frequent shots (often about weekly) with gradually increasing doses over roughly three to six months.
• The maintenance phase spaces shots out to about every 2 to 4 weeks, and the overall course usually lasts three to five years.
• Allergen immunotherapy is described by allergists as the treatment that actually changes the immune response, and benefits can persist after the course ends.
• Because there's a small risk of anaphylaxis after an injection, allergy shots are given in an allergist's office and you're asked to wait afterward for monitoring.

How Allergy Shots Work

Allergy shots deliver gradually increasing amounts of the specific allergens you're sensitive to, injected under the skin, usually in the upper arm. With repeated, controlled exposure, the immune system shifts toward tolerance rather than the allergic overreaction it would normally mount. This is why immunotherapy is often described as the only allergy treatment that changes the underlying immune response, as opposed to medications like antihistamines that relieve symptoms while you take them. The allergens used are chosen based on your history and allergy testing.

What Conditions They Treat

• Allergic rhinitis and allergic conjunctivitis (nasal and eye allergy symptoms)
• Allergic asthma, where allergens trigger asthma symptoms
• Severe allergic reactions to insect stings (venom immunotherapy is a related, specialized form)
• Sensitivities to common allergens such as tree, grass, and weed pollen, dust mites, mold, and animal dander

Shots can address several allergens at once, which is useful for people sensitive to more than one trigger. For insect-sting allergy specifically, see our insect sting allergy guide, and for asthma see managing allergic asthma.

The Two Phases and How Long It Takes

Reaching lasting benefit takes commitment, since the schedule stretches over years. Your allergist may adjust the plan if you miss doses, since gaps can change how the next dose is given.

Effectiveness and What to Expect

Allergen immunotherapy is considered the most established and effective form of allergy immunotherapy, and its benefits can persist even after the treatment course is finished. Some people also find it can reduce the chance of developing new allergen sensitivities or, in some cases, asthma. Results build gradually over months rather than immediately, so many people continue their usual allergy medications during the build-up phase and taper them as symptoms improve, guided by their allergist. An alternative for some allergens is under-the-tongue treatment; see our sublingual immunotherapy guide for how that compares.

Safety and Why You Wait Afterward

Most reactions to allergy shots are minor, such as redness or swelling at the injection site. However, because injecting an allergen carries a small risk of a severe, whole-body allergic reaction (anaphylaxis), allergy shots are given in an allergist's office, and you're asked to wait afterward — commonly around 30 minutes — so any reaction can be treated immediately. This monitoring requirement is a core safety feature of the treatment, not an optional step. See our anaphylaxis guide for what a severe reaction looks like.

When to seek care

Practical next steps

Safe general steps

1. Ask an allergist whether immunotherapy fits your allergies and goals
2. Have allergy testing so the shots can be tailored to your specific triggers
3. Plan for the time commitment of the build-up and maintenance schedule
4. Always wait the full monitoring period in the office after each shot

Actions that need medical guidance

• Deciding whether allergy shots or sublingual immunotherapy is a better fit
• Adjusting your dose after missed appointments
• Tapering allergy medications as immunotherapy takes effect

Frequently asked questions

Sources

1. ACAAI Patient — Allergy Shots (Subcutaneous Immunotherapy)
2. AAAAI — Allergen Immunotherapy
3. MedlinePlus (NIH/NLM) — Allergen immunotherapy

Medical disclaimer: This guide is for general education and isn't a substitute for personalized medical advice. It doesn't provide dosing. Always talk to a qualified healthcare professional about your symptoms and treatment.

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