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Pill Users Choose 'Wrong' Sex Partners

A woman is sexually attracted to men who smell like a good genetic match, but birth control pills make her desire the "wrong" men, a U.K. study shows.

Who is the right man? Studies suggest women are attracted to men whose genetic makeup differs from their own. Having a genetically different mate increases the chances for a healthy pregnancy and a healthy baby .

"If this really happens in the real world, women on the pill would end up choosing a more genetically similar mate than she would otherwise choose and the implications go on from there ," study researcher S. Craig Roberts, PhD, tells WebMD.

Roberts notes that in an earlier U.S. study, women who were genetically similar to their partners reported being less satisfied in their sexual relationship with their partner -- and were seeking more new sex partners -- than were women with genetically dissimilar partners.


It's true of humans, too. In laboratory studies, women who sniff men's sweaty T-shirts find them more attractive when they come from men whose MHC genes don't match theirs. It's not that certain MHC genes smell better to women -- it's the difference that counts.


"My own research says the way a man smells to a woman is the main determinant of sexual attraction," Herz tells WebMD.

In earlier T-shirt-sniffing studies, women taking birth control pills seemed to be attracted to the "wrong" men. Intrigued, Roberts and colleagues took a closer look.

They paid 37 women to smell men's T-shirts before and after going on the pill. Then they compared the women's before- and after-pill ratings of the odors to those of 60 women who did not use oral contraceptives .


Why? Roberts notes that when they become pregnant, female animals switch to preferring the scent of genetically similar males. This may allow them to seek out males that will help them protect and raise the baby. Claus Wedekind, PhD, who performed the original T-shirt-sniffing studies, has suggested that birth control pills somehow mimic this process.




Does this mean the birth control pill is a divorce pill? Herz says it's not that simple.

"A woman's response to a man's natural body odor will be colored by her feelings for him," she says. "So if you fell in love with a man online, it would be hard to be repelled by his smell."

Roberts and colleagues report their findings in the Proceedings of the Royal Society B: Biological Sciences.

(What do you think determined your choice of partner ? Talk with others on WebMD's Couples Coping message board.)

By Daniel DeNoon
Reviewed by Louise Chang
©2005-2008 WebMD, LLC. All rights reserved

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