There are few things more comforting than climbing into a bed with freshly laundered sheets. The problem, of course, is the labor involved in washing those sheets, which involves multiple trips to the washing machine, damp spots on queen-sized sets, and the task of making up the bed.

But make no mistake. You should be washing your bedsheets regularly—and not just because it makes your bedroom smell good. It’s a hygiene issue.

According to CNET, sheets collect residue from the bodies occupying them. Skin oil, dead skin cells, saliva, and sweat all accumulate. The dead skin cells are especially problematic, as they help nourish dust mites, tiny little insects that can inhabit your bed and leave tiny droppings.

Even worse, people who sleep in the buff may be leaving small amounts of fecal matter behind. At a certain point, your sheets may become the equivalent of sleeping in a six-month-old pile of dirty underwear.

Since all of this ick is largely invisible to the eye, it’s hard to tell when sheets can be officially declared "dirty," which can lead people to wind up putting off a wash. Some might opt for once a month or once a year, but that’s not enough. A better schedule for sheets is once every one to two weeks, minimum. (If you sweat, opt for once a week.) To combat the dust mites, washing in hot water (at least 130°F) is recommended. Hot water and immediate washing is also needed if you’re just getting over an illness.

Washing pillows is also advisable, though you can wait to stuff those in a washer every six months or so.

If you can’t manage to hit the washer once a week, there are things you can do to mitigate how dirty your sheets get. Showering before bed helps cut down on germs you introduce under the covers. You can also make your bed daily, which will shake loose dead skin cells. And if you have more than one sheet set, you can grab a fresh one every week, reducing the number of trips you need to take to the washer.