Question: Why do we sleep with our mouths open?

Pete Etchells answered on 26 Apr 2012:

Hey tommio! We don’t always sleep with our mouths open – sometimes they’re closed. It’s partly to do with the muscles controlling your jaw relaxing when we’re asleep – so if you’re on your back, it’s more likely that your mouth will open. I guess it’s also to do with breathing – sometimes it can be easier to draw in air through your mouth that than through your nose, especially if your nose is blocked (maybe because it’s pushing into your pillow), so you’ll open your mouth to breathe instead.