Women who take the contraceptive pill may be choosing the wrong men, according to a U.K. study.

The pill may be a "liberator" to the 12 million American women who take it, but it also may be responsible for skewing their hormones and their sense of scent causing them to choose less then perfect mates, researchers from the University of Liverpool say.

The study found that the pill can alter the type of male scent that women find most attractive, which may in turn affect the kind of men they choose as partners. It suggests that the popular form of contraception could have implications for fertility and relationship breakdowns.

The findings add to growing evidence that the hormones in the pill influence the way that women assess male sexual attractiveness.

Commenting on the study, which was published in the August issue of the Proceedings of the Royal Society, the researchers said that the pill may disrupt women’s ability to judge the genetic compatibility of men by means of their smell.

They said that this might not only impact fertility and miscarriage risk, but could even contribute to the end of relationships as women who stop or start taking the pill may no longer find their boyfriend or husband so attractive.

Researchers said the pill appears to impact the way women perceive men’s MHC genes, which play an important role in the immune system, autoimmunity, and reproductive success.

Women are often attracted to the scent of men who have MHC genes that are dissimilar to their own, according to the study. But women on the pill appear to be most attracted to men with similar MHC genes. Couples with similar MHC genes are more likely to have fertility problems, according to past research.

“The results showed that the preferences of women who began using the pill shifted towards men with genetically similar odors," said Craig Roberts, who led the study. "Not only could MHC-similarity in couples lead to fertility problems, but it could ultimately lead to the breakdown of relationships when women stop using the pill, as odor perception plays a significant role in maintaining attraction to partners.”

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