I don’t think science has an exact answer yet.
However, I was reminded of [this short SciShow video](https://youtu.be/XDaY4AzsL_8) talking about how it’s related to touching your face when you’re tired.
The implication of the video in relation to this post is that sleeping reduces the appearance of bags indirectly by causing you to touch your face less because you feel less tired.
Latest Answers