Nothing beats jumping into a bed with fresh, pleasant-smelling sheets. However, it’s likely that many Americans aren’t getting to experience that feeling quite enough. In a survey of 1,000 people, it was found that only 43% of women and 33% of men wash their sheets once a week. You may think washing your sheets every week is excessive, but that’s the frequency that is recommended. Why? According to microbiologists, it’s important to clean your bed sheets every week to prevent fungal bodies from growing in your sheets. Here’s just how nasty those uncleaned sheets can get.

More than meets the eye

Changing and washing your bedsheets is no fun. What’s even less fun, though, is the gross fungal breeding-ground your sheets become if they go unwashed. Think we’re joking? New York University microbiologist Philip Tierno says leaving your bed sheets unwashed for too long can produce the perfect medium for fungal growth. The worst part is that we can’t even see the bacteria growing in our sheets. “If you touched dog poo in the street, you’d want to wash your hands,” Tierno said. “Consider that analogous to your bedding. If you saw what was there — but of course you don’t see it — after a while, you have to say to yourself, ‘Do I want to sleep in that?'” If we had to guess, you don’t want to be sleeping in all the nastiness you can’t see.

How bacteria breeds in your sheets

So, how exactly do our bed sheets become the perfect breeding ground for bacteria and fungus? On average, humans produce about 26 gallons of sweat while they sleep each year. This sweat, in turn, seeps into your bed sheets, creating a moist environment. This environment has been coined by scientists as an “ideal fungal culture medium.” Um, gross. On top of sweat, your bed sheets can also contain microbes like animal dander, soil, lint, pollen, dust mite debris and — drum roll please — feces. All of these compounds can build upon themselves rather quickly, which is why your bed sheets need to be washed every single week.

Consequences of dirty sheets

Some of you are probably wondering just how much you can get away with when it comes to leaving your sheets dirty. Do yourself a favor and put this energy into actually washing your sheets. If the build-up of fungus and bacteria goes too long, you can actually get sick. This is especially true if you haven’t washed your bed sheets since the last time you caught a cold. Another consequence of dirty sheets is acne on the face and the back. When you sleep on dirty sheets, the bacteria in them can clog your pores and lead to breakouts. This is especially true for dirty pillow cases.

In addition, your allergies will likely be affected if you aren’t diligent about cleaning your sheets. Common allergens like dust mites and pet dander like to hang out in your sheets. What’s more, the average person sheds about 1.5 grams of dead skin cells every day. These dead skin cells are the perfect food for dust mites, and your sheets can feed a million dust mites a day on dead skin alone. Still not convinced? The allergens found in your dirty bed sheets can trigger symptoms of eczema such as dry, itchy skin. Dust mites and pet dander can also trigger asthma symptoms, causing people to have difficulty breathing throughout the day and trouble sleeping at night. So while it may be a chore to change your bed sheets every week, it’s easier than suffering from allergic reactions.