Researchers have shown that there is truth to the received wisdom that a "rosy" complexion of the skin represents healthiness, while a "green" or "pale" color indicates illness.
Lead researcher in University of St Andrews in London, Stephen from the School of Psychology, points out that several monkey species use redness in their faces or sexual skin to advertise their health status and to attract mates.
Working in collaboration with experts from the university's Perception Lab, Stephen set out to discover whether similar mechanisms were at work in humans, and how face color is associated with healthy looks.
Stephen said: "Parents and doctors know that when you get ill, you can end up looking pale. Our research goes further and shows that even young, healthy university students can benefit from a complexion reflecting more blood and more oxygen in the skin."
The university researchers claim that they are the first team to have measured how skin color varies with the amount of blood and oxygen in the blood.
The research team used computer graphics for their study, which allowed the participants to change the color of the faces in the photographs to look as healthy as possible.
For all faces, the researchers observed, the participants added more oxygen rich blood color to improve the healthy appearance.
Stephen said: "Our skin contains many tiny blood vessels that carry blood laden with oxygen to the skin cells, allowing them to "breathe", and allowing us to lose heat during exercise. People who are physically fit or have higher levels of sex hormones have more of these blood vessels and flush easier than people who are unhealthy, unfit, elderly or smokers. Physically fit people also have more oxygen in their blood than people who are unfit or have heart or lung illnesses."
Professor Dave Perrett, head of the Perception Lab, said: "Our evaluators all thought that bright red blood with lots of oxygen looked healthier than darker, slightly bluer blood with lower oxygen levels. It is remarkable is that people can see this subtle difference."
He added: "This may explain why some people with very red faces do not look so healthy; the color of their blood may be wrong. So it's not just the amount of blood that's important; it's the type of blood that determines healthy looks".
Based on their observations, the researchers came to the conclusion that people use the color of the blood in others' skins to judge how healthy they are.
"Since your attractiveness relies upon how healthy you look, you might be able to make yourself more attractive by being kind to your heart and lungs in doing more exercise or quitting smoking," concluded Stephen.
A research article on the new findings has been published in the online, open-access journal PLoS ONE.