Women are said to have an inbuilt ability to pick up the scent of a partner who differs genetically. Falling for this type of man helps ensure that the couple's children will have broad immunity against disease, so the theory goes.
But researchers found that birth controlling pills disrupt a woman's power to recognise the aroma of a compatible mate, says the study which has been published in the Proceedings of the Royal Society B: Biological Sciences.
Disturbing a woman's instinctive attraction to genetically different men could result in difficulties when trying to conceive, an increased risk of miscarriage and long intervals between pregnancies.
Passing on a lack of diverse genes to a child could also weaken their immune system.
Called the Major Histocompatibility Complex (MHC), different MHC molecules fight different diseases, so it is important to have a mix of MHC types.
Previous studies have shown that, even though humans have a relatively poor sense of smell compared with other creatures, women tend to identify partners with suitable MHC molecules - preferring males with the correct mix of immune genes critical for the survival of future offspring and to curb inbreeding, which is harmful.
To reach the conclusions, the research team analysed how the contraceptive pill affects odour preferences. In the study, one hundred women were asked to indicate their preferences on six male body odour samples, drawn from 97 volunteer samples, before and after starting to take the contraceptive pill.
They did not find that women who were not on the pill were more attracted to men with a different MHC, showing that the extent to which preferences for genetically dissimilar odours varies from study to study.
But they did find that the pill made women more likely to be attracted to a man with a similar immune makeup.
"The results showed that the preferences of women who began using the contraceptive pill shifted towards men with genetically similar odours," Telegraph quoted Dr Craig Roberts, who carried out the work in collaboration with the University of Newcastle, as saying.
"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 contraceptive pill, as odour perception plays a significant role in maintaining attraction to partners," he added.