SOMETIMES a headline stops you dead in your tracks. When I saw “Sorry Asia, you smell”, I just had to read on.

Unilever, the soap company, is poised to unleash a marketing campaign on the Asian market in an effort to persuade Asians that they need deodorants. Apparently it's a market that has proved resistant to the blandishments of soft-soapers so far. “Asians don't think they smell,” a Unilever spokesman said and, in a wistful aside, added: “but people everywhere smell”.

The human nose is incredibly sensitive, picking up odours in the tiniest quantities. We can recognise and remember more than 10,000 different smells but how we do this was unknown until the 1990s, when Linda Buck and Richard Axel, two US researchers, revealed the workings of the olfactory system. Their work earned them a 2004 Nobel prize.

Each of us has a different idea of what smells nice, and this can vary from country to country, forcing cosmetics companies to reformulate the scent of their products depending on the country to which they are marketing.

But whether we think other people smell nice or not comes down to genetics as much as anything. Our personal odour is partly determined by a diverse block of genes known as the major histocompatibility complex (MHC). One of the jobs of these genes is to help the body's immune system to distinguish our own cells from invaders. But the same genes also influence our smell. Why?In a famous experiment, women who sniffed pads wiped under men's arms found some of the niffy pads alluring, others disgusting. There was no universally approved or disapproved man whiffs; some women loved ones that others hated. But there was a pattern. For each woman, the most repellent smells belonged to men whose MHC was most similar to their own. It turns out that the more different a partner's MHC genes are from your own, the more healthy your offspring's immune system is likely to be. Human beings are engineered to choose mates whose smell is attractive, because it means healthy children are likely to result.

Smell also protects us by providing an early warning system: strangers have an unfamiliar whiff, rotting meat has an unmistakeable stench.

But Unilever may be barking up the wrong tree by taking on the Asian market. Oriental Asians (Japanese, Koreans and Chinese) have sweat glands which, even after puberty, do not produce the same type of chemicals found in other races, or produce as much sweat.

That means that Asians probably don't smell as much as Unilever might like them to. Somehow, their marketing will have to persuade them that, without their product, they won't attract the opposite sex. But given that we are all engineered to do just that au naturel, it is a fragrant irony.

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