When your bathroom exhaust fan is not functioning to its full potential, you run the risk of allowing dangerous mold buildup to take over your bathroom. Steam from showers needs to be removed as quickly as possible, which is why keeping a bathroom exhaust fan in good repair is essential for good health. One of the most important issues here is the potential presence of mold in the air duct leading out of your bathroom. Over years or even months of use, water accumulates on the outtake vents from your bathroom and mold can form. If mold forms, it should be handled carefully and by a professional with real experience. Mold is very dangerous so it should not be tampered with by an amateur. You also want to be sure that your contractor understands when it's best to repair a bathroom fan and when it's best to purchase a new one. Some contractors will just keep fixing an old fan for years because they keep getting paid for every service call. You need to be sure that you're working with a contractor you can trust and who will do what's in your best interest while working.