The secret of a man's sex appeal may lie in his cheeks, according to a study.
Researchers have found evidence to suggest a quick glimpse of a man's cheek is enough to tell women if he is attractive.
They also believe a man's complexion may somehow give clues as to whether he has "good" genes, which women unconsciously desire.
Researchers at the University of Newcastle, UK, said women had a lot in common with female peahens and mice which also use appearance to size up a male's genetic qualities.
Professor Morris Gosling and colleagues based their findings on a study of 90 women.
They were each asked to assess the facial attractiveness of 76 men.
They were then shown a small area of these men's faces and asked to rank their attractiveness again.
Assessments of healthiness and attractiveness were related to the genetic composition of these men
The rankings were the same in both tests.
The researchers then carried out DNA tests on the men. They found that men with a good mix of genes were most likely to have been ranked as attractive.
This genetic variation was found in the part of the genome that is responsible for the immune system.
"Their assessments of healthiness and attractiveness were related to the genetic composition of these men," Professor Gosling told BBC News Online.
"The genetic variation was in the part of the genome that codes for immune function."
He said the findings suggested the women were looking for healthy partners with genes that would complement theirs.
"Women choose men who are distantly related to themselves. This is perhaps to avoid inbreeding and to ensure they have good genetic diversity and are better able to face diseases," he said.
"Perhaps women choose healthy men because they believe they will live longer and will be there to help them to raise children.
"They may also see these men as being more resistant to diseases and less likely to pass on illness to their offspring.
"There are direct benefits for the female."
The findings were presented at the Royal Society's summer science exhibition in London, which runs from 1 to 3 July.