The T-shirt study also found that women taking hormonal contraception were attracted to men who had similar MHC as they did. "If you're on the pill, your body is being tricked into think you're pregnant, so you're not ovulating," Dr. Berman says. "The bad news there is that they have looked at these couples who have similar MHC, and not only do they have higher levels of infidelity and higher levels of marital discord, but they also have higher infertility issues."
Another unexpected factor that has been found to directly affect attraction is voice pitch. Dr. Gordon Gallup, a professor at the State University of New York at Albany, says that women with higher estrogen levels have higher voices, which makes them more desirable to men. "When females are midcycle, when they're the most fertile, the most likely to conceive, their voices are rated as being significantly more attractive," he says.