A survey by a British mattress company reveals something that would make many people cringe. Single men between the ages of 18 and 25 only change their bed sheets every three months on average. By comparison, single women tend to put clean sheets on the bed about every two weeks. Roughly half the single guys in the every-three-months category said they didn't see a problem with that sheet-changing timetable. Nearly 20-percent of that group said they simply don't care. "Good Housekeeping" recommends washing the sheets at least every other week.