Pill can lead women to the 'wrong' partner

TAKING the contraceptive pill can lead a woman to choose the "wrong" partner, a new study suggests.

The pill is thought to disrupt an instinctive mechanism that brings together people with complementary genes and immune systems.

By passing on a wide-ranging set of immune-system genes, they increase their chances of having a healthy child who is not vulnerable to infection. Couples with different genes are also less likely to experience fertility problems or miscarriages.

Women are naturally attracted to men with immune-system genes different from their own because of their smell, experts believe.

The major histocompatability complex (MHC) cluster of genes, which helps to build proteins involved in the body's immune response, also influences smell signals called pheromones.

Although pheromones may be almost unnoticeable at a conscious level, they can exert a potent effect.

A man's pheromonal odour is partly determined by his MHC. From a woman's point of view, a man with an alluring smell is also likely to have suitable immune-system genes.

The new research provides evidence that the contraceptive pill can upset this process.

One hundred women were asked to "sniff" six male body-odour samples from 97 volunteers and say which they preferred. The test was carried out before and after the women had started taking the pill. The study leader, Dr Craig Roberts, of the University of Liverpool, said: "The results showed that the preferences of women who began using the contraceptive pill shifted towards men with genetically similar odours."

He 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."