Will an air purifier help prevent sinus infections?
are you sure its not allergies? Is the humidifier in your bedroom because that's where you spend the most time. Do you ONLY stay in your home or do you go out to a job? If you get sick often, you are catching this from other people. Try this: Wash hands before eating or touching your face. Use a humidifier in your bedroom. Eat more vitamin C containing foods. Talk to your doctor about allergies. even in winter, allergies can strike. An air purifier will only do so much and won't effect you at all if you are out among a lot of other people.
A humidifier, particularly a cool mist one, is a breeding ground for mold and allergens. Yes, an air purifier will help. Get a good one, and one for each room.