Whether you’re checking into a two-star hotel or a five-star one, a little blind faith is always necessary. Even in the swankiest of resorts, you can never know for sure how thoroughly your room was cleaned after the last guest checked out.

You might think that you’ll be able to identify a bed that’s been rolled around in, but it’s not always obvious.

Unless the previous guest leaves a note, of course.

That’s what happened to a Reddit user who climbed into a bed at the Courtyard Marriot only to find a note that read, “If you’re reading this, then housekeeping did not change your sheets.”

How common are uncleaned hotel rooms? It’s hard to say. While online reports and reviews like the one above are common, there’s no way of knowing for sure.

Moreover, a room may appear clean while hiding more than a few stains. Back in 2006, ABC News Primetime investigated 20 well-known hotels in some of the country’s largest cities, using a black light to uncover lurking stains.

In New York City, the black light uncovered urine-stained walls and a semen-stained a bedspread at one $300-per-night hotel room.

Another hotel room, in Miami, displayed an odd pattern on the carpet. The “design” turned out to be urine — either from a disrespectful guest, or an animal of some kind.

Urine stains turned out to be a common theme. At another four-star resort, the black light revealed traces of pee on the bedspread, walls, chairs, and a stool.

Other reports have confirmed similar findings. Some common sources of dubious germs and “residues” include mugs, cups, remote controls, faucets, phone receivers, light switches, and bedding.

In the Primetime investigation, the cost of the room was never a factor. The black light revealed traces of either urine or semen in all 20 rooms, which ranged in price from $55 to $400 per night.

Cleaning staff should be vacuuming, dusting, disinfecting, and changing the sheets daily, but most hotels only undertake deep cleans a few times a year. Unless, of course, the stains are obvious.

So, How Worried Should You Be?

Thinking about the invisible stains on your hotel room bedspread or carpet might be gross, but your chances of getting sick are actually extremely low. If you’re still worried, try the following:

• Remove the bedspread. Most stains and germs can be found there.
• Use sanitizing wipes to clean items likely to be touched a lot, such as light switches, phones, and remote controls.
• Keep your own hands clean. If you have germs on your hands, you’re more likely to get sick.
• Always check the bed for bedbugs. Rust colored stains on sheets and duvets can be a sign of bedbugs.