Women may be better at sniffing out biologically relevant information from underarm sweat, a US study suggests.

Researchers found it was difficult to mask underarm odour when a woman was doing the smelling, but quite easy to do so when it was a man.

They speculate that a woman's highly attuned smell radar might help her select a mate.

The study, by Philadelphia's Monell Center, appears in Flavour and Fragrance Journal.

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 olfactory cross-adaptation.

"Women perhaps need to be more discriminating when they chose who to mate with to produce offspring"
Dr Leslie Knapp
University of Cambridge

This 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.

But 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.

Lead researcher Dr Charles Wysocki, a behavioural neuroscientist, said: "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."

Male smells robust

Not only were women better smellers than men, but male odours were harder to block than female odours.

Underarm odours from the two sexes did not differ in how strong they smelled.

However 19% of the fragrances successfully reduced the strength of male underarm odour, compared to over 50% for the female equivalent.

The volunteers first sniffed vials of underarm sweat to assess the strength of the odour.

Then they continued to rate the intensity of the smell while sniffing a second fragrance for around two minutes.

A drop in intensity ratings for the underarm odour indicated that the fragrance was a successful cross-adapting agent.

Evolutionary reasons

Dr Leslie Knapp, an expert in biological anthropology at the University of Cambridge, said there were good evolutionary reasons why a woman's ability to detect body odours should be more acute, as it could literally be an effective way to sniff out a suitable mate.

She said: "Women perhaps need to be more discriminating when they choose who to mate with to produce offspring, as they invest more than males in the reproductive process.

"Men don't need to be so choosy, they have lots of sperm, and can reproduce with lots of females, but once a woman reproduces with a partner she is tied up for nine months."

Dr Knapp said there was evidence that odour gave a hint about genetic make-up. She highlighted HLA genes involved in the immune response.

She said in evolutionary terms it was desirable for a women to mate with a man whose genes were different to hers, as this was likely to produce more robust offspring.