We have to ask, because we all know that some weeks, a sheet washing is just not going to be the top priority. "This depends on a variety of factors unique to your body, metabolism, and sleep rituals (for example, whether you sleep in the nude or wear pajamas). If you tend to get hot and sweat a lot overnight, you definitely want to wash your sheets at least biweekly. If you use body lotion everyday, maybe you’ll want to wash biweekly for that reason, too. But we would suggest washing sheets at the very least once a month," say Xiong and Yu.