Quick answer: Occasional sneezing is normal, but frequent sneezing usually points to airborne irritants, seasonal allergies, or — less often — a nasal obstruction or infection.
Dust, pollen, strong perfumes, and scented candles are frequent culprits. Dogs also sneeze during play as a signal that they're excited and not being aggressive — short rapid bursts during a game are completely normal.
Watch for sneezing accompanied by nasal discharge (clear, yellow, or bloody), pawing at the nose, a bad smell, or nosebleeds. These signs may indicate a foreign object lodged in the nasal passage, a bacterial or fungal infection, or nasal polyps.
Remove obvious irritants first — air fresheners, dusty bedding, scented products. If sneezing continues for more than two days or is paired with any of the symptoms above, see a vet. A foreign object in the nose is a medical situation that needs prompt attention.
Most sneezing resolves once the irritant is removed. Persistent or symptomatic sneezing always warrants a vet visit.