Women with high levels of the sex hormone oestradiol may engage in opportunistic mating, according to a study carried out by psychology researchers at the University of Texas, US.
According to the findings of Dr Kristina Durante and Prof Norm Li, highly fertile women are not easily satisfied by their long-term partners and are motivated to seek out more desirable partners.
Durante and Li investigated the relationship between oestradiol, an ovarian hormone linked to fertility and sexual motivation in a study of 52 female undergraduates not using contraception.
The researchers measured the hormone levels of participants, aged 17 to 30, at two points during each woman's ovulatory cycle and then asked them to rate their own physical attractiveness.
Independent observers also rated the participants' physical attractiveness.
Participants then answered survey questions that measured their propensity to cheat on a partner.
The researchers found that a woman's oestradiol level was positively associated with self-perceived physical attractiveness.
Women with a higher oestradiol level also reported a greater likelihood of flirting, kissing and having a serious affair (but not a one-night stand) with a new partner.
Oestradiol levels were negatively associated with a woman's satisfaction with her primary partner and positively associated with self-perceived physical attractiveness.
The findings were published in the Proceedings of the Royal Society of London.