Beauty sleep is a real thing, according to researchers who have shown that people who miss out on sleep do appear less attractive to others.
A couple of bad nights is enough to make a person look "significantly" more ugly, their sleep experiments suggest.
Dark-circled "panda" eyes and puffy lids can even put others off socialising with you, they say.
People were rated by strangers as less healthy and approachable when they had tired faces.
The Karolinska Institute researchers says this makes sense in evolutionary terms.
"An unhealthy-looking face, whether due to sleep deprivation or otherwise, might activate disease-avoiding mechanisms in others."
In other words, people don't want to hang around with people who might be ill, whereas someone who looks energetic and fit will hold lots of appeal.