Our beds are supposed to be the most comfortable place to be at night—but what if your pillows aren’t at their freshest or cleanest? This is why the importance of good pillow hygiene can’t be understated. If your head hurts when you lay down on your pillow, that’s even more of a telltale sign that they need changing.

Here are some tips for optimal pillow hygiene, when to replace them, and how to wash them down.

How often should you replace pillows?

Chances are, you haven’t washed your pillow in a hot minute—and that’s a habit worth breaking, for many reasons. The more you use your pillow, the more likely it will be to start flattening out and losing its firmness. Not only does this contribute to a less comfortable sleep, it also can lead to pain in your neck and/or back. If your pillow is making you uncomfortable, causing your head to hurt, or is aggravating an injury, replace it without hesitation. In that case, it could be better to simply sleep without a pillow.

You’ll also be spending a lot of time with your head on those pillows, and sweating on them in the process. Stains, mould, and lumps can also appear on your pillows over time, as can a whole host of allergens—not to mention buildups of bacteria, mildew, and saliva. It’s therefore recommended that pillows be replaced every two years maximum. Some types of pillows, such as Tempur-Pedic, are hypoallergenic, which can help those who suffer from allergies to dust mites.

Why are fresh pillows so important to have?

When your pillows are at their cleanest and smell as good as new, it can be hugely beneficial both for your sleep hygiene and overall quality of sleep. Changing your pillows can also provide you with greater firmness and more support, helping you sleep even more comfortably. Not only will it also get rid of certain allergens such as dust mites, it’s an even better investment if your previous pillows have become discoloured from certain stains. If you have a down or feather pillow, you can gently machine wash them in warm water, whereas most other types of pillows are not machine washable.

Keeping it clean regularly is also a question of basic hygiene beyond sleep: studies have shown that dust mites and their poop can both make a tenth of the weight of a pillow that has been used for two years. However, if your comforter is also in need of cleaning, keep in mind that you typically don’t need to wash it more than twice annually. Remember also that you’ll want your pillows to have the right kind of filling for you—whether wool, foam, feather, polyester, or latex—so you can have your pillows provide maximum comfort in addition to newfound freshness.