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.

Washing your bed sheets about once a week ensures they stay fresh on a regular basis. Plan to add this task to your weekly cleaning schedule to help reinforce the habit. Keep in mind that you don’t necessarily need to wash sheets the same day as you strip your bed. Having a few different sheet sets on hand makes it easy to quickly swap.