Scents and sensibility: how humans sniff each other out

The world’s media smelled a story recently that put a new twist on a simple social interaction between humans.

Scientists had discovered that a handshake was more than just a form of greeting, but a way for humans to surreptitiously "sniff" each other out. In a test environment, they got people to shake hands with each other, and noticed that they were more likely to unconsciously sniff their own hands afterwards.

Was this a throwback to animal behaviour, a more highly evolved form of canine bottom-sniffing? Was it a way to seek out a potential mate, or to size up a potential enemy? Or were we just checking to make sure the other person hadn't been eating crisps before shaking our hand?

Animals rely on sense of smell for mating and for recognising other animals within their social group, and give off pheromones to trigger a response in others of their species. But humans tend to rely more on visual and aural cues. We've long accepted that our sense of smell is less keenly developed than that of other animals, but this study, by researchers at the Weizmann Institute of Science in Israel, suggests that smell might be more important to human interaction than we realise.

“It’s a good lab, and they are careful researchers. But the thing they didn’t mention was the way that we do recognise each other as individuals by smell. And part of the sniffing may have been about that,” says Dr Tristram Wyatt, a senior researcher at the department of zoology in the University of Oxford.

“We normally take much more notice of the visual cues and hearing people speak, and that’s how we recognise people, generally. But put to the test, we’re better than chance at recognising the smell left on a T-shirt. There were lots of studies done showing that parents could recognise their children, babies could recognise their parents, in every direction; grandparents too. So we’re quite good at recognising each other by smell.”

So if Barack Obama sniffs his own hand after shaking hands with Enda Kenny, the US president may simply be using his olfactory senses to confirm that the man he’s greeting really is the Taoiseach.

Same-sex sniffing

The study found that the hand-sniffing was more prevalent in same-sex handshakes, which could rule out the theory that it's a way of finding a compatible mate (although, in the case of Kenny and Obama, it could be bromance).

One thing is for certain: it’s got nothing to do with pheromones, because although insects and lower mammals such as rodents do give off pheromones, the existence of human pheromones has never been proven. Of course, that hasn’t stopped some companies from marketing products purporting to contain human pheromones and promising to turbo-charge your sex life. And it hasn’t curtailed the rise of “pheromone parties”, at which singletons sniff each other’s sweaty T-shirts in the hope of finding a compatible partner.

"There's a big difference between a pheromone, which is something produced by an animal to communicate with another animal, and the odours that you may give off that you can't help giving off, that other animals take information from. They're quite different things," says Jane Hurst, a professor of animal science at the University of Liverpool, who specialises in mammalian behaviour.

“Animals have many specific glands that have evolved entirely for that purpose. There is no other function for these particular chemicals they are producing, other than to communicate with others of their species.”

Insects such as moths emit pheromones to attract a mate from afar, and ants use them to follow their ant trails over long distances.

“We discovered one which is used by male mice to attract female mice. And we called it Darcin after Mr Darcy. Makes the males so attractive. We published our paper on that in 2010,” says Prof Hurst.

But the jury is still out on the existence of human pheromones. In a recent TedX talk, Dr Wyatt unravelled the bad science behind the study of human pheromones, and in a recent Guardian blog he exposed the "sexing-up" of human pheromones. But he's keeping an open mind about it.

“So far as humans are concerned, there is one good candidate, which is the behaviour of babies when they take milk. There’s a group in Dijon in France that have been studying the interaction between mothers and babies. And although the molecule hasn’t been identified, it looks as though there’s a secretion from every mother’s glands around the nipple, the areola glands, that seems to stimulate the baby – not just their own baby, but any baby – to start suckling.

“But so far as human sex pheromones, nothing’s been found, despite the many claims.”

So although the study on handshakes may not prove the existence of pheromones, it does show that smell might be a more important ingredient in human interaction than we previously thought.

DOWN THE PECKING ORDER THE FIFTH BEATLE OF THE SENSES

In the pecking order of the senses, smell tends to come lowest. Sight and sound get top billing, and taste and touch get their share of attention, but the importance of smell is often ignored.

“Part of the problem is that culturally we don’t give it much attention,” says Dr Tristram Wyatt of the University of Oxford. “To give you an idea about the way society has treated smell, look at the civil societies that have been set up to help people who have lost a particular sense. In the UK, the society for helping the blind was set up in the 1860s, for the deaf about 1911, but it’s not until 2012 that we have an organisation called Fifth Sense being set up to help people who have lost their sense of smell.

“We don’t seem to treat smell with the significance it deserves. But what we do know is that if you lose your sense of smell – and the commonest way is from a head injury, or there are some kinds of viral infections like flu that give a temporary loss of smell – people report that a lot of interest in their lives disappears. A lot of what we colloquially call taste in food is really smell.”

When you think about the range of smells we encounter every day, from food to fragrances, from country odours to city smells, and from the cosy scents of home to the comforting smells of our nearest and dearest, maybe we should learn to follow our noses a bit more.