Birth Control Pills Make Women Pick Imperfect Sex Partners

For decades, women have been using the contraceptive pill to protect themselves against unwanted pregnancy. But, taking the oral contraceptives could lead to women choosing the wrong partners, suggests a new study by British scientists.

Researchers at the University of Liverpool in England say the birth control pills can disrupt women’s inborn ability to pick the perfect mate. It is believed that genesdefine in the major histocompatibility complex (MHC), which controls body odour through the immune systemdefine's interaction with skin bacteria, help determine which individuals find us attractive.

Women are thought to use smell to identify people with different immune systems and complementary genes, but the researchers believe they can lose their powerful sense of smell with the use of contraceptive pills.

To reach their findings, lead researcher Craig Roberts, a lecturer in evolutionary psychology, and his colleagues from the University of Newcastle studied 100 women who were asked to sniff 100 men's sweaty shirts.

The researchers asked all the study subjects to indicate which of six male body odour samples they preferred both before and after starting to use the birth control pill. The male scents were obtained by shredding unwashed T-shirts which the men had worn for two nights. The male participants were told to avoid using deodorants and were provided with non-perfumed soap.

After carrying out the tests before and after the women had started taking the pill, the researchers found the women's preferences changed after they began taking the pill to favour men with similar odours to their own.

“We found that the preferences of women having gone on the Pill shifted toward genetic similarity,” Dr. Roberts said. The findings suggest that it is specifically the hormonal levels within the Pill that produce this effect, he added. Oral contraceptive pills combine two hormonesdefine- estrogen and progestogen- that prevent conception.

The study further found that the use of oral contraception can lead to infertility problems and can ignite some personal issues if a woman stops taking the pill.

"Not only could MHC similarity in couples lead to infertility 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," Dr. Roberts added.