You shower every day, sometimes twice a day, but when it comes to cleaning bed sheets, many people are less thorough about cleanliness. And if you’ve left your sheets for longer than a week, it’s time to get washing!

According to a YouGov poll, a third of people reveal they wash their bed sheets every two weeks, The Mirror reports. But when it comes to washing your sheets, Mary Zeitler of Whirlpool's Institute of Home Science, told Today the magic number is seven days. This makes sense, considering that the average person spends 56 hours a week on their bed sheets. These sheets are filled with dead skin cells, sweat and body oil, which build up and can result in dust mites and other allergens. Plus, it’s gross.

So gross, that there are things living in your sheets you may not have even thought of, and Philip Tierno, a microbiologist, and pathologist at the New York University School of Medicine, decided to terrify everyone when he told Tech Insider (via Science Alert): "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, sputum, vaginal, and anal excretions, urine milieu, skin cells.”

There’s also makeup and other cosmetic products, and food from people who like to eat in bed. And the publication notes that the average human naturally produces 26 gallons, or 98.4 liters, of sweat in bed every year. All of this sweat and bacteria is the perfect environment for fungus and microscopic life.

There’s also a right way to wash your sheets, and when doing a load you need to ensure that there is enough room in the washer, and definitely, no other clothes to avoid items getting bungled up. Cotton sheets, especially in lighter colors (the darker ones fade with very warm water) are safe to wash at any temperature, but it’s always smart to check the label first.

Another tip we can take from Mary Zeitler is to wash sheets on warmer temperatures during the cold and flu season to destroy bacteria.

Now, excuse me while I go wash my bedsheets!

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