Can dry mouth be caused by sinuses?

Possibly: If you have enough drainage from your sinuses that you find you are breathing thru your mouth, then it may be drying out your mouth.

Possibly: If you have significant sinus congestion where you are unable to breathe well through your nose, then you would be a mouth-breather, which will lead to dry mouth. See your internist (md) or otolaryngologist (ear, nose & throat md) to evaluate your sinus problem and determine a beneficial solution.

Dry Mouth and Sinus: If you take antihistamines to help control your sinsus problems that can certainly cause a dry mouth. Also, those with sinus issues often breath through their mouth more since their nose tends to be blocked and that can also lead to a dry mouth. Drink plenty of fluids to keep your mouth hydrated and to help protect your teeth.