A new study suggests that a lack of sleep might make other people look less attractive to you. In the study, published in the journal Nature and Science of Sleep, Swedish researchers used eye-tracking technology to determine what 45 male and female participants were looking at in real time. Participants got no sleep at all one night and eight hours of sleep another night. The researchers tracked their eye movements the mornings following both nights. Sleep-deprived participants rated angry faces as less trustworthy and less healthy-looking and fearful faces as less attractive. Overall, sleep loss was associated with more negative social impressions of others. The researchers found that when we are sleep deprived, we focus less on other people’s faces, increasing the chance that we misinterpret their emotional state.