In the new study, researchers tested how women''s sexual scent preferences changed depending on men''s levels of testosterone and cortisol.
Male volunteers were given T-shirts to wear for two consecutive nights, during which time they were prohibited from using scented soaps or detergents; drinking or smoking; or eating garlic, onion, green chiles, strong cheeses and other pungent foods.
Then, female volunteers sniffed the men''s shirts and rated the pleasantness, sexiness and intensity of the smells (on scales from 1 to 10). The women also completed a questionnaire about their stage in their menstrual cycles and whether they were using hormonal contraception.
The researchers took saliva samples from the men to measure hormone levels of testosterone and cortisol.
Women who were at the most fertile stage of their menstrual cycles preferred the smell of men with higher testosterone, rating these "manly" shirts as the most pleasant and sexiest, results showed.
The women showed no preference for the smells of men with higher cortisol levels. Without taking the women''s fertility into account, neither hormone had an influence on how attractive the men smelled.
The chemical androstenol contributes to the musky smell of body odor. Men produce much more of this chemical than women, and testosterone levels may be linked to production of these molecules, the researchers suggested.
If so, the women in the study may be responding to these subtle odor cues.
If the findings can be replicated, scientists could try to identify these odor molecules, and then figure out how they influence human scent preferences.
However, whether these chemicals are signals of masculine qualities, or just a byproduct of them, remains unclear.