The study revealed the women preferred more animated faces
Flirtatious men have a better chance of attracting a woman when she is at her most fertile during her monthly cycle, research has suggested.
Evolutionary psychologist, Dr Edward Morrison, of the University of Portsmouth, asked a group of women to examine various facial expressions.
He found when the women were ovulating they preferred flirtatious expressions.
Dr Morrison said: "If we wanted to attract someone at the Christmas party, flirting effectively may help."
He added: "An ability to 'read' and interpret the facial expressions and an awareness of what you are signalling with your own expressions could improve your chances of successful flirting.
"It is difficult to define what constitutes flirtatiousness and much of it may be something we perceive without even realising it.
"But it seems that in the absence of other cues, the 'social properties' of facial movement influences how we judge attractiveness."
As part of the study, published in Archives of Sexual Behaviour, researchers produced several animated facial models which were rated on a flirtatiousness scale by 16 women.
Then a separate group of 47 women were asked which of them they found most attractive by rating them on a scale of one to seven.
By measuring their level of movement in their faces, researchers revealed that most of the women preferred the faces that were more animated.
They also concluded that women recognise specific "mating-relevant" social cues.
However, Dr Morrison added: "Science is still a long way from discovering the magic formula for what women find attractive in a man."