These ugly, microscopic cousins of spiders are the prime source of year-round allergies. Researchers estimate that 20 million Americans suffer from dust mite allergies. Perfectly adapted to the temperature and humidity of a typical home, dust mites survive on the tiny flakes of skin that all of us shed each day. An adult typically sheds enough skin each day to feed a million dust mites.

A protein in the mite's waste products—not the mite itself—is what provokes allergic reactions. A single dust mite may produce as much as 200 times its body weight in waste. Bedrooms have been shown to be the main repository of dust mites in a typical home. To reduce the effects of dust mites there:

• Cover pillows and beds with zipped dust-proof covers.
• Wash sheets in hot water (at least 130 degrees Fahrenheit)
• Reduce and/or eliminate "dust catchers" such as stuffed toys, draperies, comforters and wall-to-wall carpeting.
• Equip vacuum cleaner with special filters. Vacuum bedding thoroughly. One researcher suggests vacuuming a single mattress for 20 minutes regularly to reduce hidden dust mites.