Getting a good night’s sleep has been linked to improved athletic performance and cognitive function. It’s also believed to influence our appearance, leading to the popular notion of “beauty sleep.” But does sleep deprivation actually play a role in the way we look?

As an experiment, Greg and Mitch from the AsapSCIENCE channel decided to stay awake for 36 hours, taking photos every 6 hours to track whether a lack of sleep had any impact on their appearance.

“Scientists don’t actually know why we look so messed up when we don’t sleep,” says Greg, citing the two most popular theories from evolutionary biology which might explain it.

The first theory goes that when you are sleep-deprived, you have a weakened immune system and are more prone to accidents. Having this weakened state reflected in your face lets other well-rested members of your community know to avoid you. The second theory suggests that being deprived of sleep makes you more pessimistic, and less adept at exhibiting emotion.

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