For many travelers, hotel hygiene is a touchy subject.

“If you’re reading this, then housekeeping did not change your sheets!” the note reads.

That’s a bit disturbing, but also anecdotal. To take a slightly more scientific approach, Inside Edition checked into nine hotel rooms, then used a stencil and a non-toxic fluorescent paint to write “I Slept Here” on all of the bed sheets.

The show’s investigators found that three of the nine hotels didn’t change the sheets.

Aren’t hotels required by law to change their bedsheets?

No, not really. While laws vary from state to state, hotels can generally set their own laundry policies. Even when housekeepers forget the fresh sheets, the risk of a serious health problem is low.

In 1992, the American Hotel & Lodging Association noted that the Centers for Disease Control and Prevention (CDC) “has NEVER identified, seen, or classified ANY significant disease outbreak in hotel or motel rooms as a result of hotel bedspreads and blankets.” Still, the CDC notes that laundering clothes can limit the spread of various communicable diseases including the norovirus.

How can you make sure that you’re sleeping on fresh sheets?

First, don’t necessarily assume that the price of the room reflects the quality of the cleaning service. A 2016 study found that three-star hotels seemed to have fewer germs in four- and five-star hotels.

“Camera exposés have revealed hazardous cleaning techniques, such as hotel personnel wiping the countertop with the same towel used to clean the toilet,” the study noted. “Though many types of bacteria don’t pose health risks, it’s always a good idea to be cautious and prepared.”

Some hotel chains have taken steps to ensure cleanliness. Since 2006, the 1,900-location Hampton Inn chain has changed sheets on a daily basis. Recently, Hampton Inn housekeepers have started putting sticky notes on the sheets to prove to guests that they’re clean.

Marriott Hotels have laundered all of their bedding on a daily basis since 2005, according to the chain’s vice president of operations, John Whitwell.

“We clean all the sheets and duvet covers and anything that touches the guests,” Whitwell said.

If you’re worried about getting clean sheets, inspect your bedding thoroughly right after checking in. If you notice anything alarming, insist on new bedding. Before staying in a hotel, you can call ahead to ask for a bed with an allergy barrier, which will help if you’re especially sensitive to allergens.

The good news is that most modern hotels seem to change their sheets. The bad news? You’re going to have to take their word for it.