“I can’t sleep without it,” you exclaim as you clutch the pillow you’ve slept on for the past decade.

Sorry to say, but it’s probably time. The older the pillow gets, the less it keeps its shape and structure. As a consequence, it begins to be unable to do its primary functions—keeping your spine in a neutral alignment and helping you get a good night’s sleep. Generally, pillows should be replaced between every 18 to 36 months, depending on the quality of the pillow.

As a rule of thumb, that’s good, but what else should you be looking out for?

Give it a folding test

Your pillow in its prime should maintain the shape it was in after you first broke it in. To get a sense of how its holding up, fold your pillow in half and then release it. If it goes back to its regular shape, it’s still good to go. If it keeps looking like someone karate-chopped your pillow, consider replacing it. This is especially true for fluffier pillows, like feather pillows. 

It’s visibly looking dirty

Overtime, your pillow will have accumulated a history of your face—dead skin, body oils. Some of these stains can be washed away, but once you start to see permanent scars of sleepy time on your pillow, that’s a sign that you should do away with it. Though, on its own, stains don’t mean as much as the folding test above.

While an aesthetically unpleasant pillow on its own seems harmless, you’re inviting dust mites that are going to find your pillow to be appetizing. It’s obviously gross to sleep on these micro dinner guests, and they’re also common causes of allergies, which might get you sneezing in your sleep.

You keep waking up with aches and pains

If you’ve been using ol’ reliable for awhile and you start feeling strange bouts of neck pain, it’s most likely that the pillow is losing its support and structure during the night. This may not have been an issue when your pillow was young and spry, but with time, it’ll start to flatten out and not be able do its job. When it’s letting you down, it’s time to let go.

There are more telltale signs, which have less to do with the pillow and more with you. For example, if you’ve changed up your favorite sleeping position, a new pillow that is compatible with your new position is needed. To get searching, here are the top four things to know when pillow buying.