©Aubrey Edwards/CorbisForty pounds of dust; that's how much dust collects every year in the average American six-room house [source: Berger]. Now, your dorm room isn't nearly as big as a house in the suburbs but it still collects big amounts of dust -- in fact, your average used mattress (welcome to dorm life) may itself have between 100,000 and 10 million dust mites living inside [source: Lyon]. First things first: Dust isn't dirt -- this isn't a matter of your roommate's muddy boots. Bedding, too, is also a major contributor to the dust in your dorm room, and all sheets, blankets, and pillowcases should be washed in hot water -- or changed, at least -- every week. Finally, a fan-style air purifier will help reduce dust levels in your room -- and will help with odor control in general [source: U.S. EPA].