Allergy shots work by gradually exposing your immune system to increasing amounts of the substances that trigger your allergies, training it to stop overreacting. The process takes three to five years, but about 60% of people who complete the full course experience permanent relief even after stopping treatment.
What Happens Inside Your Immune System
When you have allergies, your immune system treats harmless substances like pollen, dust mites, or pet dander as threats. It produces large quantities of a specific antibody that latches onto these allergens and triggers the cascade of symptoms you know well: sneezing, itching, congestion, watery eyes. Allergy shots intervene at the root of this process rather than just masking symptoms.
Each injection delivers a tiny, controlled dose of your specific allergens. Over time, this repeated exposure prompts your immune system to generate specialized regulatory cells that act like a dimmer switch on the allergic response. These cells suppress the inflammatory signals that would normally be sent to the parts of your immune system responsible for allergic reactions, including the cells that release histamine.
The regulatory cells also shift which type of antibody your body produces in response to allergens. Instead of making the antibody that triggers allergic symptoms, your immune system starts producing a “blocking” antibody called IgG4. This blocking antibody intercepts allergens before they can set off a reaction. Think of it as your immune system learning to neutralize the allergen quietly instead of sounding a five-alarm response every time pollen lands in your nose. Specialized immune cells that produce this blocking antibody become essential players in building long-term tolerance.
The Two Phases of Treatment
Allergy shot treatment is divided into two distinct stages: a buildup phase and a maintenance phase.
During the buildup phase, you receive injections one to two times per week, with each shot containing a slightly higher dose of allergen than the last. This phase typically lasts several months as your allergist gradually increases the concentration until you reach what’s called your maintenance dose, the level that provides therapeutic benefit without causing significant reactions.
Once you hit the maintenance dose, you shift to receiving shots about once a month. This phase continues for three to five years, sometimes longer for people with severe allergies. The full course of treatment is essential. Stopping early, even if you feel better, increases the chance that your symptoms will return because your immune system hasn’t had enough time to build durable tolerance.
How Long Until You Feel a Difference
This isn’t a quick fix. Most people start noticing a reduction in symptoms six to eight months into treatment, often while still in the buildup phase. Some take a full 12 months before improvement becomes noticeable. The most significant relief typically arrives during the second year of treatment, as your immune system’s shift toward tolerance deepens.
After completing three to five years of maintenance shots, some people find their allergy problems are gone for good. Others need ongoing shots to keep symptoms controlled. There’s no reliable way to predict beforehand which group you’ll fall into, but completing the full recommended course gives you the best odds of lasting results.
What the Shots Can (and Can’t) Treat
Allergy shots are effective for environmental allergens: pollen (tree, grass, weed), dust mites, mold, pet dander, and insect venom allergies. They’re commonly used when antihistamines and nasal sprays aren’t providing enough relief, when you want to reduce your dependence on daily allergy medications, or when your allergies trigger asthma symptoms.
They are not used to treat food allergies. Food allergy immunotherapy exists but uses different approaches and protocols. Both children and adults can receive allergy shots, though they’re not typically recommended for children under age five because younger kids may have difficulty cooperating with the injection schedule and articulating symptoms if a reaction occurs. For older adults, conditions like heart disease need to be evaluated first since reactions can put extra stress on the cardiovascular system.
Risks and the Observation Period
Because you’re being injected with the very substances your immune system reacts to, there is a real, if small, risk of allergic reactions to the shots themselves. Local reactions at the injection site, like redness, swelling, and itching, are common and generally mild.
Systemic reactions, where symptoms spread beyond the injection site and can include hives, shortness of breath, or in rare cases anaphylaxis, occur in roughly 0.7% of injections under standard scheduling. That’s why you’re required to wait in the clinic for at least 30 minutes after each shot. Most adverse reactions appear within that window, and your allergist’s office is equipped to treat them immediately. This waiting period is non-negotiable at every appointment for the entire duration of treatment.
The Practical Cost Commitment
Beyond the time investment, allergy shots carry a financial one. Most insurance plans cover immunotherapy but charge a copay per injection. Those copays, often $20 per shot, add up quickly when you’re going weekly. If your allergist splits your allergens into two separate injections per visit (which is common for people allergic to multiple things), you could be paying $40 per session.
Over the full course of treatment, out-of-pocket costs can range from roughly $3,000 to over $6,000 depending on your copay structure, how many injections you receive per visit, and how long your maintenance phase lasts. Insurance coverage varies dramatically between plans, so it’s worth getting specifics from your insurer in writing before starting. Factor in the time cost too: weekly clinic visits during the buildup phase, each requiring a 30-minute post-injection wait, mean a significant schedule commitment for months before you transition to monthly visits.
Why the Full Course Matters
The immune changes that allergy shots produce are gradual and cumulative. The regulatory cells and blocking antibodies your body builds need sustained reinforcement to become your immune system’s default response to allergens. Stopping after one or two years, when you’re feeling better but haven’t completed the full course, is like pulling a plant out of the ground before its roots are established. The tolerance you’ve built can fade, and your original allergic responses can return.
For people who stick with the full three to five years, allergy shots remain the only widely available treatment that can fundamentally change how the immune system responds to allergens rather than simply suppressing symptoms. That distinction is what makes the time and cost worthwhile for many people: the possibility of walking through spring without reaching for a tissue.