The results of the study show 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 also was associated with paler skin, more wrinkles or fine lines, and more droopy corners of the mouth. People also looked sadder when sleep-deprived than after normal sleep, and sadness was related to looking fatigued.
Lead author Tina Sundelin, MSc, lead author and doctoral student in the department of psychology at Stockholm University in Stockholm, Sweden, said that 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.
She said that this is relevant not only for private social interactions, but also official ones like with health care professionals and in public safety.
In the study - conducted at the Karolinska Institute in Stockholm, Sweden - Ten subjects were photographed on two separate occasions: after eight hours of normal sleep and after 31 hours of sleep deprivation.
The photographs were taken in the laboratory at 2:30 p.m. on both occasions. Forty participants rated the 20 facial photographs with respect to 10 facial cues, 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 judgments of attributes such as trustworthiness, aggressiveness and competence.
The study has been published in scientific journal Sleep.