One of the best parts about staying at a hotel is not needing to clean. But when you leave the job up to other people, you can't be sure if it's actually being done.

Many people don't sleep with the comforter of their hotel beds, because it's common knowledge those big blankets don't get cleaned every day. But do you fully trust the sheets are freshly clean? Even at a nice hotel, clean sheets for every new guest may not be the norm.

A secret investigation

Inside Edition revealed alarming results when they carried out an experiment testing for sheet cleanliness in hotel rooms. They booked hotel rooms for one night, marked the sheets, and then checked into the same rooms the next night under different names to see if the marks were still there.

Disgustingly, several hotel rooms they tested were caught with dirty sheets.

At each hotel, when the first Inside Edition investigator checked into their room, they laid a large stencil on the bed's sheets and sprayed the stencil with harmless, washable fluorescent paint. The words "I slept here" were big and bold, but could only be seen with a UV light.

The next night

The next morning, the first investigator checked out, and another Inside Edition investigator under a different name checked in to take a look at the sheets. If the hotel service actually changed their sheets between each guest, either the invisible message would have been washed away or a new, clean pair of sheets would have replaced the marked ones.

At the first hotel, reporter Ann Mercogliano whipped back the comforter with a UV flashlight in hand to see the large stencil mark still there. She called a manager up to her room to disclose the disgusting situation.

"This sheet hasn't been changed. Why weren't the sheets changed?" Mercogliano asked the manager.

The frazzled manager responded, "OK, I expect them to be changed every day, and that is a policy of our property."

The results

At each hotel Inside Edition checked (and caught with soiled sheets) the managers and maids claimed their policy is to change the sheets between each and every guest and they didn't know why those particular sheets weren't clean.

But three out of the nine hotels Inside Edition tested were caught with dirty sheets, suggesting a pattern rather than a random, rare mistake.

The three hotels Inside Edition caught with dirty sheets were the Candlewood Inn & Suites near Manhattan Times Square, a La Quinta Inn & Suites by Central Park and Residence Inn by Marriott also near Times Square (a hotel rated One Diamond by AAA). But this pattern of uncleanliness most likely has more to do with each individual hotel's management and not the chain as a whole.

The health risk

Numerous studies reveal that homeowners should be washing their sheets once a week or so. Philip Tierno (a microbiologist and pathologist at the New York University School of Medicine) outlines what's hiding in your dirty bed sheets: "You have spores of fungi, bacteria, animal dander, pollen, soil, lint, finishing agents of whatever the sheets are made from, coloring material, all sorts of excrements from the body including sweat". Yikes.

It's gross enough you're sleeping in this germ cocktail in your own home, but at least you know where the dirt and fungi came from - you! Obviously, you wouldn't want to crawl into a bed that someone else had been sleeping in.

How can I make sure mine are clean?

Unfortunately, you can't be sure whether your hotel room's sheets are dirty or not (unless there is a visible stain or mark). But if you want to make sure you aren't sleeping in a stranger's used sheets, there are a couple of ways to avoid it.

When you first check in, ask maid service to bring you an extra set of sheets, then change the mystery ones for the fresh ones.

Or, (and this might sound a bit crazy, but many people do it), bring your own sheets from home.

The next time you take your family to a hotel, remember there's a decent chance the sheets are still dirty from the last family.