Do Allergy Shots Have Side Effects? Yes — Here's the Full Risk Context

This is difficult to answer precisely because local injection-site reactions — the most common side effect — vary widely in how they are defined across studies. If we define 'no side effects' as no local reaction at all, roughly 14-74% of patients fall into this category depending on the study methodology. Most patients experience at least mild injection-site redness or itching at some point during treatment, particularly during build-up when doses are increasing. No systemic reactions occur in more than 99.8% of injection visits. Patients who complete the full treatment course without any notable side effects do exist — but some degree of local immune response is expected and actually indicates the immune system is recognizing the allergen extract as intended.

By absolute risk metrics, allergy shots have a lower fatal reaction rate than many accepted medical procedures and common medications. The modern SCIT fatality rate of approximately 1 per 9 million injection visits (Epstein 2019, JACI Pract) compares favorably to other routine interventions. For context, the anaphylaxis fatality risk from penicillin is estimated at roughly 1 per 50,000-100,000 courses. The key difference with SCIT is that fatality risk is concentrated in identifiable high-risk patients — particularly those with uncontrolled asthma, who accounted for 88% of confirmed immunotherapy fatalities (Bernstein 2004, JACI). Pre-screening for asthma control and other risk factors effectively stratifies and manages this risk.

Yes — allergy shots are elective, and you can decline if the risk profile does not feel acceptable to you. That said, your allergist can help contextualize the risk relative to your specific allergy burden. Alternatives exist: sublingual immunotherapy (SLIT) drops and tablets offer a disease-modifying option with a lower systemic reaction profile, though with fewer available allergens. Daily antihistamines and nasal corticosteroids manage symptoms without disease modification. The right choice depends on the severity of your allergies, your asthma status, which allergens are driving your symptoms, and your personal risk tolerance. Patients should never feel pressured to accept SCIT if the risk-benefit balance does not feel right for their situation.

Yes — asthma is the most important risk factor for severe allergy shot reactions. In the Bernstein 2004 JACI fatality survey covering 41 deaths over 12 years, 88% of fatalities occurred in patients with asthma, most of it suboptimally controlled. An analysis of near-fatal reactions (Amin 2006, JACI) found that 40% of near-fatal reactors had baseline FEV1 less than 70% predicted — meaning lung function below that threshold substantially increases the risk of respiratory decompensation during a reaction. This is why allergists require asthma to be well-controlled before each injection, and why pre-injection peak-flow assessment is recommended for asthmatic patients. Well-controlled asthma does not preclude SCIT — but uncontrolled asthma is a genuine contraindication.

The AAAAI/ACAAI 2011 Practice Parameter is clear on this: allergy shots can be continued but are not typically initiated during pregnancy. This distinction matters. Patients already at maintenance dose may continue safely — studies including Metzger 1978 (121 pregnancies), Shaikh 1993 (109 pregnancies), and a Swedish registry analysis (Larsson 2022; 743 AIT-exposed pregnancies from 924,790 total) found no increased risks of congenital malformation, preterm birth, or stillbirth in women receiving immunotherapy. However, dose increases are avoided during pregnancy because a systemic reaction could cause fetal hypoxia or uterine contractions. If you become pregnant during the build-up phase at a sub-therapeutic dose, your allergist will typically recommend pausing or holding at the current dose rather than continuing to escalate.

Long-term safety data for allergy shots are reassuring. The 2011 AAAAI/ACAAI Practice Parameter found no new long-term safety signals after prolonged maintenance therapy. A Danish nationwide registry study (Linneberg 2012, JACI) comparing SCIT-treated patients with pharmacotherapy-only patients found SCIT was actually associated with lower autoimmune disease risk, lower acute MI risk, and lower all-cause mortality — not an increase. No increased cancer risk has been demonstrated in SCIT-treated patients. The PAT Study (Jacobsen 2007, Allergy) followed children through a 10-year follow-up after SCIT and found the primary long-term effects were beneficial: reduced asthma development (25% vs 45% in controls) and fewer new sensitizations.