Why do my car windows fog up?

I realize why the windows fog up but the fog just doesn't go away. When I get in the car, the windows are typically fine. As I go down the road, the fog slowly increases. Even when turning on the front and rear defrost, the windows are still foggy! The front windshield is usually fine at this point, but the sides and rear gl are not. I've tried cleaning the windows and everything but no progress. The windows are tinted, which I don't know much about, I bought the car that way. Any ideas? This really affects my visibility on the road.. Thanks!