Can Allergy Shots Cause Sinus Infections? The Surprising Truth

No — allergy shots do not cause sinus infections. SCIT works by modulating the immune response from Th2-dominant allergy to Treg-mediated tolerance. This process does not suppress pathogen defense or impair the immune system's ability to fight bacteria or viruses. Unlike corticosteroids, which broadly suppress immunity and can increase infection susceptibility, allergen immunotherapy selectively re-educates the allergic immune response while leaving innate and adaptive pathogen defense intact (Akdis & Akdis, JACI, 2015). If you experience sinus infections during SCIT, the allergy itself — which is still being treated during build-up — is the most likely cause of continued sinusitis.

Sinus infections during SCIT build-up almost always reflect the underlying allergic rhinitis rather than the treatment itself. During build-up, SCIT has not yet reached therapeutic dose — typically taking 3–6 months to reach maintenance concentrations. Until then, allergic nasal inflammation continues, blocking sinus drainage and creating conditions for bacterial sinusitis. This is the same sinusitis pattern you would experience without treatment — the allergy shots haven't made it worse; they simply haven't fully corrected it yet. As SCIT reaches maintenance phase and nasal inflammation decreases, sinusitis frequency typically falls. If sinusitis was a major problem before starting SCIT, document your frequency before and after treatment to see the long-term improvement.

Evidence suggests that long-term SCIT reduces sinusitis frequency in allergic patients. A retrospective study by Hankin et al. published in JACI (2013) found reduced antibiotic prescription rates for sinusitis in patients who completed 3+ years of allergen immunotherapy, consistent with the mechanistic expectation. SCIT reduces allergic nasal inflammation and mucosal edema — the primary drivers of sinus ostia obstruction and secondary bacterial sinusitis. After reaching maintenance dose and achieving sustained immune tolerance, patients with allergic rhinitis-driven sinusitis should experience fewer episodes. SCIT is specifically recommended in patients with allergic rhinitis who develop recurrent sinusitis as a downstream complication.

Allergic rhinitis causes sinus infections through a well-established causal chain: allergen exposure triggers mast cell degranulation in the nasal mucosa, releasing histamine and leukotrienes that cause mucosal edema and mucus hypersecretion. The paranasal sinuses drain into the nasal cavity through small openings called ostia, which are typically 2–6mm in diameter. When allergic nasal edema narrows or blocks these ostia, mucus cannot drain normally and accumulates in the sinus cavities. The stagnant, warm, low-oxygen environment favors bacterial overgrowth — primarily Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis — producing acute bacterial sinusitis (Fokkens et al., EPOS 2020). This is why allergic rhinitis is a major risk factor for chronic rhinosinusitis.

Yes — chronic sinusitis with an allergic component is actually one of the stronger indications for allergen immunotherapy, not a contraindication. If your chronic sinusitis is driven by underlying allergic rhinitis (documented by allergy testing), SCIT addresses the root cause in a way that antihistamines, nasal steroids, and antibiotics cannot: by modifying the allergic immune response itself. Patients with chronic rhinosinusitis with nasal polyps should be aware that polyps may have a component independent of IgE-mediated allergy — SCIT addresses only the allergic contribution. Nasal corticosteroid sprays remain first-line for polyp management and are complementary to SCIT rather than competing with it. Discuss the allergic vs non-allergic components of your chronic sinusitis with your allergist for a personalized plan.

Many allergists recommend holding allergy shot doses during active acute sinusitis, particularly if the patient has fever, facial pain, purulent discharge, or feels acutely unwell. The rationale is that systemic immune activation from the infection may lower the threshold for allergic reactions during SCIT, and administering shots during illness makes it harder to distinguish infection symptoms from injection reactions. Additionally, some allergists prefer the immune system to be in a more stable state during dose escalation. Individual protocols vary — some practices hold shots only during fever or antibiotic treatment, while others continue if symptoms are mild. Contact your allergist's office before attending for a shot during an active sinus infection, as they will advise based on your specific situation and dose history.