Lack of sleep really does make you less attractive, according to scientists studying the "negative effects of restricted sleep on facial appearance and social appeal".

In the study, published in Royal Society Open Science, researchers discovered that a few nights of bad sleep can make you appear significantly less attractive to others, as well as less healthy. In even more bad news for poor sleepers, they found that people are less inclined to want to socialsze with you if you're tired.

The Karolinska Institute in Stockholm sent 25 university students home with a kit to measure night-time movements and check they were getting the amount of sleep they reported they were. The students were asked to get a good night's sleep for two nights in a row. After that, they were photographed by the researchers.

A week later, they were asked to restrict themselves to a measly four hour's sleep for two nights in a row. After this, they were photographed again. The researchers then took to the streets of Stockholm to show the two sets of photographs to 122 strangers, asking them a range of questions from "how much would you like to socialise with this person in the picture?" to "how trustworthy is this person?"

The team, lead by Dr Tina Sundelin, found that strangers were good at assessing how tired a person was, and that they rated the sleepy set of photographs as less attractive than the photos of the same people when they were well-rested. In short, people can tell when you're tired and think you are less attractive when you haven't got enough sleep.

The authors said that their findings made sense in evolutionary terms. "An unhealthy-looking face, whether due to sleep deprivation or otherwise, might activate disease-avoiding mechanisms in others," they wrote. Basically, when you see someone who looks sick, the last thing you want to do is hang out with them.