The sweet smell of sweat

Technologist, May 23 2015

Everyone knows that animals use odours to communicate. Now a growing body of research suggests that humans do, too.

Taking a long, deep whiff of someone’s dirty laundry may not sound like the ideal way to start a hot date. But if the latest evidence is anything to go by, the time has come to reconsider that strategy. The primal smell of a potential partner’s body odour may be just the trick to finding out how compatible you really are.

This discovery has not been lost on those touting “pheromone perfumes” on the Internet, or those behind the growing popularity of “pheromone parties”. At these events, partygoers each sleep in a t-shirt for three nights before handing it in, unwashed, at the door. The idea is that, guided by their noses rather than their eyes, attendees sniffing these sweaty garments will choose suitable matches.

Whilst it has long been known that many animals, including mammals such as rodents, rely heavily on their sense of smell for mating strategies, the idea that humans can do the same inspires scepticism. Yet a growing body of evidence is beginning to reveal just how sensitive humans are to chemical cues released in body odour.

“I’ve been doing research in smells since the early 70s and I’ve seen a remarkable change,” says Charles Wysocki of the Monell Chemical Senses Center in Philadelphia. “A lot more information is becoming available to show that humans are processing odours even though they may not consciously be aware of it.

Smell or smartphones?

Whether to find a mate, warn others of danger or identify prey, animals use smells to communicate a wealth of information to others of the same species. Humans, on the other hand, have long underestimated the importance of body odour. A recent survey of more than 7,000 young people around the world found that half would rather give up their sense of smell than their smartphones.

It is no surprise then that our olfactory sense has been undervalued compared to other senses that seem to be more essential to human survival. After all, we pay little attention to odours unless we suddenly encounter a particularly wretched one. And people find it much harder to identify fragrances – putting a name to them or detecting exactly where they come from – than they do sounds and sights.

The idea that humans may have pheromones – small chemicals or compounds that trigger a social response in other members of the same species – has come into favour largely thanks to research led by biologist Claus Wedekind at the University of Bern in 1995. His experiments were the precursors to pheromone parties: female students were asked to rate the smell of sweaty t-shirts that men had worn to bed.

Wedekind’s “sweaty t-shirt” study found that women preferred the smell of garments worn by men whose immune systems were significantly different from their own, as measured by a set of molecules called the Major Histocompatibility Complex (MHC).

Mating with someone with a different immune system could be evolutionarily advantageous for adapting to selection pressures in the environment, such as pathogens. The finding led the authors to conclude that humans had evolved a way of sniffing out a good mate...