People also looked sadder when sleep-deprived than after normal sleep, and sadness was related to looking fatigued, scientists said.
Sleep deprivation affects facial features such as the eyes, mouth and skin, and these features function as cues of sleep loss to other people.
Researchers from the Karolinska Institute in Stockholm, Sweden, found that the faces of sleep-deprived individuals were perceived as having more hanging eyelids, redder eyes, more swollen eyes and darker circles under the eyes.
Sleep deprivation was also associated with paler skin, more wrinkles or fine lines, and more droopy corners of the mouth.
"Since faces contain a lot of information on which humans base their interactions with each other, how fatigued a person appears may affect how others behave toward them," said Tina Sundelin, lead author and doctoral student in the department of psychology at Stockholm University in Stockholm, Sweden.
"This is relevant not only for private social interactions, but also official ones such as with health care professionals and in public safety," Sundelin said.
The study photographed 10 subjects on two separate occasions: after eight hours of normal sleep and after 31 hours of sleep deprivation. Forty participants rated the 20 facial photographs with respect to 10 facial fatigue and sadness.
According to the authors, face perception involves a specialized neuronal network and is one of the most developed visual perceptual skills in humans. Facial appearance can affect judgements of attributes such as trustworthiness, aggressiveness and competence.


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