"It is quite difficult to block a woman's awareness of body odour. In contrast, it seems rather easy to do so in men," said study lead author Charles J. Wysocki, PhD, a behavioural neuroscientist at Monell.
The researchers speculate that females are more attuned to biologically relevant information in sweat that may guide women when choosing a mate.
In the study, women and men rated the strength of underarm odours, both alone and in conjunction with various fragrances.
The fragrances were selected to test their ability to block underarm odour through a method known as cross-adaptation. Olfactory adaptation refers to the loss of sensitivity to an odour when one is constantly exposed to that odour. Olfactory cross-adaptation occurs when the nose adapts to one odour and then also becomes less sensitive to a second odour.
Sniffed alone, the underarm odours smelled equally strong to men and women. When fragrance was introduced, only two of 32 scents successfully blocked underarm odour when women were doing the smelling; in contrast, 19 fragrances significantly reduced the strength of underarm odour for men.
Wysocki noted that in earlier studies, men and women did not differ in their ability to cross-adapt to odours not from the body.
"Taken together, our studies indicate that human sweat conveys information that is of particular importance to females. This may explain why it is so difficult to block women's perception of sweat odours," he said.
Not only were women better smellers the men, but male odours were harder to block than female odours. Even though underarm odours from the two sexes didn't differ in how strong they smelled, only 19 percent of the fragrances successfully reduced the strength of male underarm odour; in contrast, over 50 percent decreased intensity of female underarm odour.
In the study, one sensory panel evaluated fragrances for their ability to counteract female underarm odour; a second panel judged the effectiveness of fragrances against male odour. Each panel contained both men and women.
To make their odour evaluations, panelists sniffed vials of underarm sweat previously collected in the laboratory from volunteers.
Panelists first rated the intensity of underarm odour to provide a measure of the odour's strength. They then continued to rate underarm odour intensity while sniffing a fragrance for 2-1/2 minutes.
A drop in intensity ratings for the underarm odour indicated that the fragrance was a successful cross-adapting agent, capable of neutralising the odour.
"Men and women differ in how they perceive body odours from both their own and the opposite sex," summarised Monell scientist George Preti, PhD, an analytical organic chemist who co-led the research with Wysocki. "Women are more aware of underarm odour and they appear to be detecting differences in odour quality."