Researchers have discovered the perfect "flirting face" used by women who want to date a man.
Women are likely to use common facial cues to demonstrate sexual interest in a way that can be seen and understood by men.
The surefire flirting techniques include a head turned to one side and tilted down slightly, a slight smile, and eyes turned toward the implied target, the study found.
This kind of identifiable facial expression is most likely to activate associations with relationships and sex in the male brain.
Omri Gillath, professor of psychology at University of Kansas, said: ""There are very few scientific articles out there that have systematically studied this well-known phenomenon.
"None of these studies have identified the flirting facial expression and tested its effects."
In some of the studies, professional actresses and volunteers were asked to pose a flirting expression or to follow instructions for what researchers define as flirting.
The team found some women were more effective than others in conveying flirting, while some men are better at recognising it.
But beyond some individual differences, a few expressions were identified by the men as flirting.
Published in the Journal of Sex Research, the researchers used the Facial Action Coding system to define the perfect "flirting face" that would be recognised by men as showing attraction.
Dr Gillath said: "Across our six studies, we found most men were able to recognise a certain female facial expression as representing flirting.
"It has a unique morphology, and it's different from expressions that have similar features -- for example, smiling -- but aren't identified by men as flirting expression.
"Our findings support the role of flirtatious expression in communication and mating initiation.
"For the first time, not only were we able to isolate and identify the expressions that represent flirting, but we were also able to reveal their function -- to activate associations related with relationships and sex."
