Actors and actresses from Hollywood already know the secret. Penelope Cruz and Catherine Zeta-Jones swear by its ability to make them look young and radiant. Clinical studies prove it to be true. Is it the newest make-up or plastic surgery? No, it's just a good  night of sleep. Turns out that sleeping well not only impacts overall health, it also affects how we look. Here's how:

Our brains are prewired to be very perceptive to faces. In fact, we have a special part of our brain that is dedicated to nothing other than recognizing differences in facial appearance. That's why even if two people share very similar features (such as same hair color, same head size, same eye color, etc.), we can still easily tell them apart. That's also the reason why we can detect when someone is not feeling well. If you've ever been on the receiving end of the statement, “You look tired today," chances are you already know that fatigue can be pretty apparent.

How exactly does sleep play a role in our facial appearance?

There are a variety of studies that examine what parts of our face are affected when we are sleep-deprived. A recent study, published in the journal  Sleep, took a dive into the visible impact sleep deprivation can have on physical appearance. The study compared photos of people after they had eight hours of quality sleep compared and then after 31 hours of sleep deprivation. Photos taken of people after sleep deprivation were noted to have saggy eyelids, more redness in the eyes, dark circles under the eyes, as well as eye swelling. Perhaps even more interesting was that their skin appeared paler, wrinkles were more prominent, and people appeared to look sadder than they did in the rested photos.

Why does sleep have such a strong impact on our appearance?

We know that getting sleep not only rests the mind but also the body. It gives the body a chance to repair damage. New collagen forms, helping your skin look young and firm. Sleep loss can also cause blood vessels under the eyes to dilate, giving them the dark appearance. Finally, lack of sleep can also affect your mood, which clearly shows up on your face. More research is needed to fully understand the factors that link sleep to appearance.

How much sleep is enough to look your best?

One study suggested that slightly over nine hours of sleep each night was associated with the best appearance. In reality, there probably isn't one right number. The key is getting the amount you need to feel fully refreshed, and for most adults, that's between seven and nine hours. However, getting more sleep than your body needs doesn't mean you're going to keep getting more attractive. After all, even if I slept 16 hours a day, I'm not going to magically turn into Brad Pitt (right?). The key is to avoid skimping on the shut-eye, so you can look your personal best.

The next time you see an eye-catching face walking down the street that looks energetic and happy, remember that beauty sleep is a real thing based on research. Sure, maybe they're born with it, but it could also just be a good night's sleep!