Quick answer: Occasional sneezing is normal, but persistent sneezing in cats usually points to an upper respiratory infection, irritant exposure, or — less commonly — nasal polyps.
The most common cause of repeated sneezing in cats is viral upper respiratory infection (herpesvirus or calicivirus). Symptoms include sneezing, nasal discharge (clear or colored), watery eyes, and sometimes a mild fever. Very common in cats from shelters, rescues, or multi-cat households.
Dust from litter, scented candles, air fresheners, and household cleaners are frequent triggers. If your cat sneezes more after you clean, change litter brands, or burn candles, irritant exposure is the likely cause. Try unscented litter and eliminate strong fragrances near the litter area.
See a vet if sneezing is frequent (more than 5-10 times per day), lasts more than a few days, or is accompanied by colored nasal discharge, loss of appetite, or eye discharge. Bacterial secondary infections may require antibiotic treatment.
Most sneezing from viral causes resolves with supportive care. Remove irritants first. Persistent or symptomatic sneezing needs vet evaluation — colored discharge almost always indicates a secondary infection.