Does the sweaty stink of a man's used t-shirt reveal more about him than his personal hygiene habits? According to UK researchers, the answer is yes.
Psychology researcher Craig Roberts, from the University of Stirling, and colleagues, have that found women's preferences for male body odor are constant over time.
That constancy suggests a man's unique underarm aroma might provide women with important biological clues about his suitability as a life partner, they write in the latest issue of the Flavour and Fragrance Journal .
The researchers asked six male "odor donors" to wear a cotton t-shirt to bed for two nights. The men avoided garlic, smoky rooms and smelly cheese for two days prior and steered clear of deodorants, aftershaves or perfumed soaps.
The researchers then asked 63 heterosexual women aged between 18 and 32 to sniff the t-shirts and rate them on a score from 1 to 7, where 1 was "not at all pleasant" and 7 was "extremely pleasant"
The women were also asked "Is this how you would like your long-term partner to smell?" and then ranked the t-shirts in order of preference.
About three months later, the process was repeated with the same male "donors" and female sniffers, and a new batch of t-shirts.
"Women scored the six male odors consistently across the two tests," the researchers write. The most popular smell scored an average of 5.5 out of 7, and the least pleasant scored just 2.33.
Similarly, the women's ranking of the scents in terms of potential partners also remained steady between the two tests.
The fact that the women's preferences remained constant indicates there are "underlying genetic contributions to individual body odors," the researchers say.
This also suggests that humans use body odor in much the same way as other animals, where smell helps signal aspects of a potential mate's quality, they say.
"Our results ... lend weight to the assumption that body odor constitutes a meaningful cue of quality that can be used in individual assessment during human interactions," they conclude.
The results build on a growing body of evidence that humans use smell to help select their sexual partners, as do many other animals, said Rob Brooks, a professor of evolutionary biology at the University of New South Wales.
There's accumulating evidence that people are able to use smell to identify partners who have a good genetic match in a set of immune system genes called MHC, Brooks said.
The MHC genes code for a set of immune cell molecules that help the body identify and kill bacteria and other pathogens.
"The best thing is to have a MHC genotype that's dissimilar to yours. That way, the kids have... a more diverse array of immunological tools with which to fight off infection."
"We don't have as potent a sense of smell as some other animals," said Brooks. "But smell is still important to us."