Women with high levels of the hormone estradiol tend to be less satisfied with their partners and more likely to cheat, according to new research published today in the Royal Society's Journal Biology Letters . They are also considered to be significantly more attractive by themselves and by others.

Scientists from the University of Texas measured levels of the hormone in 53 women aged 17 to 30. The women were then asked to rate how attractive men find them, compared to other women, before their photograph was rated by a panel of men and women. The researchers asked other relevant questions, such as how many partners the women had had and how often they sought long- and short- term relationships.

Those subjects in a relationship also rated their commitment to their partner, how satisfied they were both emotionally and sexually, and how likely they were to flirt with other men or cheat on their partner in the coming year.

The results showed that women with higher estradiol levels were more likely to flirt, kiss or have a serious affair with a man outside of their primary relationship, but were not more likely to indulge in a one night stand.

The reproductive benefits of estradiol are well documented. Not only do women with higher levels of the hormone tend to have larger breasts, a low waist-to hip ratio and attractive faces - all attributes which draw attention from the opposite sex, they are also found to have higher mating standards - picking men with high testosterone levels.

The most surprising finding was that the women were more likely to cheat, but not indulge in casual sex. The authors believe the reason to be that attractive women unknowingly capitalise on their looks by repeatedly trading their partners for a better long-term mate when the opportunity arises.

But although hormones can underlie the motives behind women's mating choices, they might not control them directly. Further research will provide a better understanding of the relationship between our hormones and our life decisions.

The Royal Society