Your bed alone, if it is averagely clean, averagely old, averagely dimensioned, and turned averagely often (which is to say almost never) is likely to be home to some two million tiny bed mites, too small to be seen with the naked eye but unquestionably there. It has been calculated that if your pillow is six years old (which is the average age for a pillow), one-tenth of its weight will be made up of sloughed skin, living and dead mites, and mite dung--or frass, as it is known to entomologists.