Your bed gathers all sorts of dirt, oil, and sweat while you sleep. Learn how often to wash bedsheets so you can sleep soundly on fresh bedding.

You typically spend upwards of eight hours in bed each day, which leads to the buildup of dirt, body oils, dead skin cells, sweat, and other grime on your sheets and bedding. All this residue isn’t just gross to think about; it can also provide fodder for dust mites, put extra strain on the fabric’s fibers, and trigger health issues including allergies, skin irritation, and acne—not exactly ideal for a peaceful night’s sleep.

The average person changes their sheets about every 24 days, according to a recent survey by Mattress Advisor. But that’s not the best schedule for optimal hygiene and freshness. How often you should wash your sheets depends on a few factors, but there are some general rules that work for most people. Read on to learn exactly how often to wash your sheets, as well as how to preserve their freshness if you decide to bend the rules a bit.