The feel of a freshly made bed is like no other. If getting into bed every night is one of life's fine treats (and I believe it is), then slipping between newly clean sheets is like the organic dark chocolate version of that treat. 

On the flip side, bed-making is time consuming, so doing it takes time away from doing other, more fun things. And then there's all the laundry generated by changing sheets, creating even more work. 

Not surprisingly, when it comes to a household chore that's a Venn diagram of small enjoyments, cleanliness, and time, there are plenty of opinions on how often it should be done (or if it gets done). 

I was raised to shower each night before bed, to only ever wear pajamas in bed, and the house I grew up in was cold at night (no night sweating). I am a deep sleeper, and one who enjoyed a king-sized bed my entire childhood and young adulthood. Plus, I don't move much at night, so I changed my sheets every three or four weeks until I left for college. There I saw crazy things, like people not making their beds in the morning, getting into bed with outside clothes (not pajamas), and even putting their dirty socks under their bedcovers. And of course there was the guy who slept directly on the mattress and by the end of the year it was covered with a body-sized stain. (That image will stay with me forever — along with the horrific odor.) I was shocked as those things seemed irredeemably filthy.

Of course what's "dirty" is a subjective thing. But the truth is that your body does let go of hair, dead skin, and exudes oils and bacteria when you sleep (not to mention dust mites and what your dog or cat may leave behind if they sleep with you), so all those things need to be cleaned off of sheets because otherwise, quite simply, they start to smell. 

These days, we change the sheets more often in my bedroom — every 10 days to two weeks. That's because I share a very small (double!) bed with a tall man who sweats the night away, tosses and turns, and showers in the morning, which to me equals "goes to bed dirty." (At least there are still no outside clothes in the bed.) 

But when I inquired on Facebook about this, other people's answers were all over the map. "Once a week. More if hygiene dictates: Ex. sex," said Jenn, a recent PhD grad in her mid 30s. Another young woman and man had similar replies about it depending on if they had a partner in the bed or not, so it seems that young, sexually active folks might change their sheets most often. 
"Usually every two weeks since I sleep alone and don't sweat. It's rarely hot enough! I hang my sheets out, even in winter," says Mave, a retired Portland, Oregon, woman. 
Jonah, who is in health care sales, was thinking about water use when it came to his housecleaning choices: "Once every two weeks. I'd probably do it once a week, but who has that time and it uses a lot of water. Living in Cali for so many years I try to conserve the resource when possible." 
Turns out my Facebook friends are on target, though in a poll over at the Ask a Clean Person column on Gawker, a full third of respondents to a poll said they went a month or more between sheet changes. I'm just going to say it — that's too long.
Good Housekeeping advises: "Bed sheets should be washed at least every other week. If you sweat at night, wash your bed sheets weekly." They also say you should wash pillows and comforters two to three times a year, which was surprising to me. I triple-line my pillows with case-liners and wash those regularly, but have never washed a pillow in my life. I wash my comforters and blankets once a year — and never wash duvet inserts at all; I hang them outside for 24 hours in a very sunny spot in the spring when I take them off my bed and then store them for the year. (Should I rethink this?) 
Martha Stewart thinks we should change them more often — but then she would, wouldn't she? "In general, it's a good idea to launder them weekly to remove dirt and dust. Use warm water rather than hot, which can shrink fibers, and wash printed and colored pillowcases inside out to protect the color. If your sheets feature delicate trim, check the care label before washing." Quite sensible, but I don't have that kind of time, Martha! I'm just not as much of a perfectionist as you are, though I will agree with you about the proper way to fold a fitted sheet, because it's the exact same way my grandma taught me. 
So it seems like the two-week rule is a good one (says me), balancing keeping clean with the work (laundry and bed-making) taken up by changing sheets. But there are a few reasons to change more often. As Good Housekeeping reminded me, you should always change sheets after you've been ill, and the more you sweat at night, whether from hot nights or because you are a night-sweater generally, the more often you should change your sheets. 
Your personal schedule should take into account: How many people are in your bed at night? A single adult, or a couple with a kid (or two)? Pets? Are they under or on top of the covers? Do you sleep naked or in pajamas? Do you sweat? Do you eat in bed? 
How often do you change your sheets, and why? 

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Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.