'If you look back in history, It's a common double standard of society, The guy gets all the glory the more he can score, While the girl can do the same and yet you call her a whore,' sings Christina Aguilera in Can't Hold Us Down.

London - Women who have many sexual partners are disliked by other women - but men who are sexually voracious are less likely to be judged by their peers.

A study found that promiscuous females – defined those who had slept with 20 people by their early 20s – were more likely to be rejected as a friend by another woman.

Experts are not sure exactly why this is, but they believe the behaviour has evolved as an attempt to keep relationships safe.

Interestingly, a woman's preference for less sexually active friends even remained when the female questioned reported having liberal attitudes to casual sex or a high number of lifetime lovers.

But the research, carried out by Cornell University developmental psychologists, found that the results were far less striking when men were surveyed.

Researchers found that most men were no more or less likely to be friends with a peer who had a lot of lovers.

The study, titled ‘Birds of a Feather? Not When it Comes to Sexual Permissiveness’ also says that loose women may be at greater risk of being socially isolated and at greater risk of poor psychological and physical health.

“Sexually permissive women are ostracised for being 'easy,' whereas men with a high number of sexual partners are viewed with a sense of accomplishment,” said lead author Zhana Vrangalova.

“What surprised us in this study is how unaccepting promiscuous women were of other promiscuous women when it came to friendships – these are the very people one would think they could turn to for support.”

The findings show that although attitudes about casual sex have relaxed in recent decades, women still face a double standard that shames “easy” women yet celebrates “studly” men, said Vrangalova.

She suggested that women may be seeking to distance themselves from any stigma that is attached to being friends with such women.

The researchers explained that it may be evolutionary concerns that is leading women and a number of men to disapprove of their bed-hopping peers as friends.

They may actually be seeking to guard their partner from a threat to their relationship, Vrangalova added.

She added that previous research has shown that men often view promiscuous women as unsuitable for long-term romantic relationships, leaving these women outside of many social circles.

“The effect is that these women are really isolated,” Vrangalova said.

She said that future research to determine whom they could befriend was needed – and suggested making friends with straight or gay men who would be accepting of their behaviour.

The study involved 751 university students who provided information about their past sexual experience and their views on casual sex.

They read a near-identical short story about a male or female peer, with the only difference being the character's number of lifetime sexual partners - two or 20.

Researchers asked them to rate the person on a range of friendship factors, including warmth, competence, morality, emotional stability and overall likability.

Across all female participants, women – regardless of their own promiscuity – viewed sexually permissive women more negatively on nine of ten friendship attributes, judging them more favourably only on their outgoingness.

Sexually permissive men only identified two measures - mate guarding and dislike of sexuality - where they favoured less sexually active men as friends, showing no preference or preferring the more promiscuous men on the eight other variables; even more sexually modest men preferred the non-permissive potential friend in only half of all variables.

The study was published in the online Journal of Social and Personal Relationships - Daily Mail