It has been known that women get sexually attracted to the men who smell like a good genetic match, men whose genetic makeup differs from their own because having a genetically different partner increases the chances for a healthy pregnancy and a healthy child. Previous studies have shown that women, whose genetic make-up was similar to their partners, were less satisfied in their sexual relationship and were further looking for new partners, genetically dissimilar.

A U.K. study shows that birth control pills may be tricking the woman into choosing the "wrong" man.

Animal studies have confirmed that female mammals smell out males whose MHC genes are different from their own and by mating with such partners, they give their offspring a better disease-fighting characteristics. The same goes for humans.

Researchers say there is a real connection between body odor, MHC, and the mates a woman chooses. T-shirt-sniffing studies have shown that women who sniff men's sweaty T-shirts find them more attractive when they come from men whose MHC genes don't match theirs.

The same studies have shown that womnen who were taking birth control pills at the time of the study seemed to be attracted to the "wrong" men, so the researchers decided to take a closer look.

They chose 37 women who were to smell men's T-shirts before and after going on the pill and then have their before- and after-pill ratings of the odors compared to those of 60 women who did not use oral contraceptives. The results were clear. After going on the pill, women chose genetically similar men while women who did not take the pill had increased preferences for genetically different men.

A possible explanation connects the state of pregnancy with the state of a woman on birth control pills. When pregnant, female animals seem to prefer the scent of genetically similar males as they are looking for males that will help them protect and raise the baby.

But what happens when a woman taking birth control pills marries a man to whom she's attracted -- and then stops taking the pill. Independent of the study, marriage counselors report that the No. 1 complaint among women no longer sexually interested in their husbands is that they can no longer stand how they smell and if you can't stand how someone smells, you cannot be intimate.