Proof That 'You Look Tired' Is an Insult

"You look tired." Those are the last three words any of us want to hear when trudging into work, bleary-eyed and groping for coffee. Yet new research suggests that not only can people detect sleep loss just by looking at you, but when they see it, they're less inclined to want to be around you.

A study published in the journal Royal Society Open Science builds on earlier work by researchers at Sweden's Karolinska Institute showing that sleep-deprived people appear less healthy and less attractive compared to their well-rested counterparts. The new study replicates that earlier finding and shows that people are less likely to socialize with people they perceive as sleep-deprived.

Researchers asked 25 university students, both male and female, to get eight hours of sleep two nights in a row. (They were given devices that tracked their movements to confirm they'd gotten a good night's sleep.) A week later, they were restricted to four hours of sleep for two consecutive nights.

After each session, researchers took photos of the sleepers and tried to make things as consistent as possible—everyone wore a dark gray t-shirt, relaxed their face (no smiling), and posed make-up free with their hair back and with minimal jewelry. Photos were then shown to 122 raters, who judged the photos on attractiveness, health, sleepiness, and trustworthiness. Interestingly, while people rated photos of the students when they were sleep-deprived lower on both health and attractiveness (sigh), they weren't seen as less trustworthy. Still, raters were less inclined to want to socialize with them.

The study authors note that, for better or worse, we tend to ascribe positive characteristics to attractive people: We assume they're more sociable and competent at interpersonal relation, while. And sleep-deprived people actually are more accident-prone, less optimistic and sociable, and less able to read and express emotions, so you can see why, theoretically, they don't make for great pals.

But there may be another reason we seem to shy away from the zombies among us. Humans have evolved to avoid disease; we keep our distance in the face of possible contagion. In this line of thinking, lack of sleep can look like poor health. So in addition to appearing less attractive, tired people may be seen as less healthy, and even contagious. "Having an unhealthy-looking face, whether due to sleep deprivation or otherwise, might thus activate disease-avoidance mechanisms in others and render one's surroundings less socially inclined," as the authors put it.

All of this judgment happens largely without thinking, and these descriptions of it are based in evolutionary psychology. And while it's intuitively persuasive—it sounds like a scientific explanation for the notion of "beauty sleep"—it's also based on a data from a relatively small number of young Swedes. Still, it's something to consider next time you're looking at yourself in the mirror after an ill-advised all-nighter.

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