We don't need to tell you that sleep is important — everyone knows that. It's the reason you sometimes have to skip a girls' night or finish a work project in the a.m. instead of staying up late. But, aside from giving you the ability to function properly, sleeping seven to nine hours a night also allows for much-needed repairs to happen on the cellular level.
To understand why hitting that sweet spot is so important, we went to Dr. Jessica Wu, a board-certified dermatologist based in Los Angeles. She confirmed what we always knew: Beauty sleep is an actual thing — if you go through each of the five stages of sleep, that is. "Not hitting all the stages, which last an average of 90 minutes each," she says, "means you're not getting all of the benefits of sleep."
So, what is it exactly that our skin does at night, and how does sleep help? From info on boosting collagen production to tips for hydrating overnight with a sleeping mask, like Olay Regenerist Luminous Overnight Mask, here's what you need to know. Only thing we're not sure about? If sleep is a viable excuse for being late.