Allergy shots are a long-term treatment that gradually trains your immune system to stop overreacting to specific allergens like pollen, pet dander, dust mites, mold, and insect venom. Unlike antihistamines and nasal sprays that temporarily mask symptoms, allergy shots target the underlying cause of your allergies and can provide relief that lasts years after you stop treatment.
How Allergy Shots Retrain Your Immune System
When you have allergies, your immune system produces a type of antibody called IgE in response to harmless substances like grass pollen or cat dander. These IgE antibodies sit on the surface of immune cells called mast cells and basophils. When the allergen shows up again, it locks onto those antibodies, triggering the cells to release histamine and other chemicals that cause sneezing, itching, congestion, and swelling.
Allergy shots work by introducing tiny, controlled amounts of the allergen under your skin, prompting your immune system to shift its response. Over time, specialized immune cells called regulatory T cells push your B cells to produce a different antibody, IgG4, instead of IgE. IgG4 acts as a blocker. It competes with IgE for binding to the allergen, essentially intercepting it before it can trigger histamine release. This blocking effect also disrupts a cycle where allergen-IgE complexes on B cells keep amplifying the allergic response. The result is a gradual dampening of your allergic reactions at their source.
What Allergies Can Be Treated
Allergy shots are effective for a specific set of environmental and venom allergies. According to the American College of Allergy, Asthma & Immunology, they work well for reactions to trees, grass, weeds, mold, house dust, animal dander, and insect stings. They’ve also been proven effective for allergies to ragweed relatives, including avocado, melon, and some other fruits.
They’re commonly prescribed for allergic rhinitis (hay fever), allergic asthma, eye allergies, and stinging insect allergies. However, allergy shots are not used for food allergies (other than those cross-reactive fruit allergies mentioned above) or for drug allergies. If your primary triggers are environmental, you’re a good candidate.
The Two-Phase Treatment Schedule
Treatment happens in two distinct stages, and the full commitment typically spans three to five years.
The first phase is the buildup. Over three to six months, you receive shots one to three times per week, with each injection containing a slightly higher dose of allergen than the last. This gradual escalation is what allows your immune system to adjust without triggering a serious reaction. Once you reach your target dose, you transition into maintenance.
During the maintenance phase, you receive one shot per month. This continues for three to five years, sometimes longer. Each visit requires you to stay at your allergist’s office for about 30 minutes afterward so staff can monitor you for any reactions.
When You’ll Start Feeling Better
Allergy shots are not a quick fix. Most people start noticing a reduction in symptoms six to eight months into treatment, often while still in the buildup phase. For others, it takes a full 12 months of regular injections before improvement becomes noticeable. The benefits then continue to build over the following years of maintenance.
This slow timeline is one reason people abandon treatment early, but completing the full course matters significantly. Studies show that courses shorter than three years are associated with symptom relapse within a year of stopping. Sticking with treatment for at least three years is the threshold for achieving lasting benefit.
How Well They Work
Clinical trials consistently show allergy shots outperform placebo, though the degree of improvement varies by person. In one study of grass pollen immunotherapy, 65% of treated patients achieved clinically meaningful improvement compared to 35% on placebo. Physician assessments in the same trial found significant symptom improvement in about three-quarters of treated patients versus roughly a third of placebo patients, with a corresponding drop in the need for rescue medications like antihistamines.
For many people, allergy shots don’t eliminate symptoms entirely but reduce them enough that daily medications become unnecessary or can be significantly scaled back. The treatment is also one of the few interventions shown to prevent the development of new allergies and reduce the risk of allergic rhinitis progressing to asthma in children.
How Long the Benefits Last After Stopping
One of the most compelling reasons to consider allergy shots is their durability. Evidence shows that three years of immunotherapy produces tolerance that persists for at least two to three years after you stop treatment. Some people maintain benefits much longer.
A five-year study that included a three-year treatment phase followed by two years of follow-up found that symptom scores remained 25 to 36% lower in the immunotherapy group compared to placebo across all five consecutive pollen seasons, including the two years after treatment ended. This kind of lasting effect is something no daily allergy medication can offer.
That said, some patients do eventually see symptoms return, particularly if their course of treatment was on the shorter side. If relapse occurs, a second course of immunotherapy is an option.
Risks and Side Effects
The most common reaction is redness, swelling, or itching at the injection site. These local reactions are frequent, occurring in roughly 5 to 9% of all injections for most patients.
Systemic reactions, where symptoms affect more than just the injection site, are rare. A large surveillance study covering more than 1.1 million injections found systemic reactions occurred in just 0.025% of injections, or about 1 in every 4,000 shots. These reactions can range from mild hives or nasal congestion to, in very rare cases, anaphylaxis. This is why you’re required to wait at the office after each injection.
One useful predictor: patients who develop large local reactions (significant swelling at the injection site) are more likely to eventually have a systemic reaction. If you consistently get large welts after your shots, your allergist may adjust the dosing schedule.
Allergy Shots vs. Sublingual Immunotherapy
Allergy shots (subcutaneous immunotherapy) aren’t the only form of allergen immunotherapy. Sublingual immunotherapy, which involves placing a tablet or drops under your tongue daily at home, is an alternative for certain allergens. Sublingual tablets are currently available for grass pollen, ragweed, and dust mites.
Both approaches produce lasting tolerance when used for at least three years. The main trade-offs: allergy shots cover a wider range of allergens and can be customized to your specific triggers, but they require frequent office visits. Sublingual tablets are more convenient since you take them at home, but they’re limited to a few specific allergens and can’t be combined the same way shots can. Your allergist can help determine which option fits your allergy profile and lifestyle.