Sleep wrinkles aren't your average fine lines: While expression lines can form overtime from repeatedly moving your face, these wrinkles form exclusively from your sleeping positionsay, if you curl up on your side or sleep on your stomach, face smashed into the pillow. That's why one study on facial aging identified a distinct set of wrinkles that form from sleep alone, which brings us to the anecdotally dubbed "sleep wrinkles."

It makes sense, no? If you sleep with your face smashed into the pillow for eight or some hours each night, that's quite a long time for the delicate skin on your face to endure that pressure. Not only that, but the skin is more permeable at night, which means it is more vulnerable to transepidermal water loss (also why you might opt for a heavier night cream to seal in moisture; nighttime skin care is no joke). This means your skin is not only experiencing friction, but may dry out faster, too. All things considered, of course you may wake up to some folds across your skin.

Now, those indents tend to fade when you're young, as your plump skin is chock-full of collagen and can quite literally bounce back from the pressure. (Think of a firm mattress molding to your weight as you sleep, then filling out once you leave your cozy bed.) But as you grow older and your collagen levels start to decline, you may notice those lines stick around well after midmorning.

See the article here:
So Sleep Wrinkles Are A Thing: Here's What It Says About Your Skin - mindbodygreen.com