Contraceptive pills may disrupt women's innate ability to sniff out a genetically compatible partner, say UK researchers.
A team led by Dr Craig Roberts at the University of Newcastle reports its findings online ahead of print publication in the journal Proceedings of the Royal Society B.
Previous studies suggest that women are instinctively attracted, via their sense of smell, to men who have a dissimilar genetic makeup.
This is possibly because an overly similar gene profile can result in difficulty trying to conceive a child, an increased risk of miscarriage and a weaker immune system.
A group of about 140 genes in an area called the Major Histocompatibility Complex (MHC), which helps build proteins involved in the body's immune response, plays a key role in odour through interaction with skin bacteria.
Scientists believe how these genes are expressed may help determine how individuals sniff out mates. Testing responses to male scents
Roberts and team conducted an experiment to find out if taking the pill influences odour preferences.
One hundred women were asked to indicate which of six male body odour samples they found most attractive, both before and after starting to take the contraceptive.
The male scents were drawn from 97 volunteers.
"The results showed that the preferences of women who began using the contraceptive pill shifted toward men with genetically similar odours," says Roberts.
The researchers say they are not sure if the change in preference related to pill use is sufficiently strong to influence partner choice.
But, if odour does indeed play significant role in mate choice then their findings suggest the pill could induce women to pick 'Mr Wrong'.
Not only that but it could have further implications.
"It could ultimately lead to the breakdown of relationships when women stop using the contraceptive pill, as odour perception plays a significant role in maintaining attraction to partners," says Roberts.
The study also found women in relationships expressed a greater preference for odours of MHC-dissimilar and unfamiliar men, a result consistent with studies in birds.
Oral contraceptives combine two hormones, oestrogen and progestogen, to inhibit normal female fertility.
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