Being sleep deprived could lead to some uncomfortable social encounters. A new study published in the journal Neurobiology of Sleep and Circadian Rhythms suggests that when we’re sleep deprived, we have a harder time recognizing when people are happy or sad.

The researchers, led by University of Arizona psychologist William D.S. Killgore, showed photographs of the same male face expressing six different emotions to 54 participants. There were 180 photos total, some with very obvious displays of emotion and others with more subtle signs.

When participants were sleep deprived, they had a harder time recognizing “more subtle expressions of happiness and sadness,” according to the study press release. (Their social sussing abilities came back after a good night’s rest). When they were sleep deprived, participants could still recognize obvious expressions like anger or fear though, something Killgore suspects is due to survival instincts: We’re hardwired to recognize emotions we perceive as threats.

While recognizing happiness and sadness may not be crucial to our immediate survival, it has a marked impact on our human experience, namely our ability to correctly read and respond to those around us. For example, being able to tell if your boss is mildly pleased or slightly disappointed by your recent project.

If we’re not sleeping enough, we lose the ability to read the “emotions that make us human,” Killgore said, and may be less empathetic as a result. He concludes that, “to me, that is one of the biggest problems [with lack of sleep] — how this affects our relationships.”

You should always aim for a good night’s sleep for selfish reasons like your own physical and mental health. But if all else fails, catch some zzz’s to be more perceptive in your social life — those you interact with will thank you.

Read the press release here.

Originally published at