A new study suggests that taking the contraceptive pill can inhibit a woman's sense of smell, causing her to choose the "wrong" partner.
Experts believe that women are naturally attracted to men with immune system genes different from their own because of the subtle smell signals, or pheromones, they give off.
The pill is thought to disrupt this instinctive mechanism after a study showed that the preferences of women who began using the contraceptive shifted towards men with genetically similar odours.
Couples with different genes increase their chances of having a healthy child that is not vulnerable to infection, and are also less likely to experience fertility problems or miscarriages.
A man's pheromonal odour is partly determined by his major histocompatability complex (MHC) - a cluster of genes which helps build proteins involved in the body's immune response and which also influences pheromones.
The new research provides evidence that women who take the contraceptive pill - which simulates a state of pregnancy - can fail to pick up on the pheromonal signals.
Study leader Dr Craig Roberts, from the University of Liverpool, said: "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."