Pit's a Wonderful Life

It sounds like something out of a science fiction horror, but we humans have all sorts of microorganisms living on our skin and inside our bodies. In our armpits, microbes metabolise the food we give them, producing a distinctive smell. But one man's B.O. is another's bonding mechanism, as Rob Dunn explains to Chris Smith... 

Rob - We're really a collective. All of our attributes of our bodies that we think of as the function of our own cells really are more often collaborations and antagonisms between our cells and the microbes on our skin, the microbes in our guts, the mites that live on our faces and all over our bodies. This is inconspicuous when we look at each other with our eyes, but if you close your eyes and you sniff people, almost all the smells of humans are microbial. To the extent that you love the smell of your partner or you hate the smell of your partner, I hope you don't hate the smell of your partner, but if you do, it's really a very direct manifestation of this cooperative between our cells and these microbial cells.

Chris - I interviewed a researcher for the journal eLife a few years ago when he published this paper. When I first read it, I thought it couldn't be real. He did a study where they had cameras set up to watch two people meeting each other. One was in on it and other people just thought they were coming to be interviewed about something random. They had rigged these people up with a system to measure when they sniffed. Some of the time the interviewer that they were meeting shook their hands and other times they purposefully didn't shake their hands. The hand that had been shaken spent significantly longer in front of the person's face coinciding with sniffing than other times in the interview. He said it was really funny because he presented this at a conference and he said, he then went to the party in the evening where it was a meet and greet or 'get to know each other' time welcome drinks. He said everyone was walking around with their hands in their pockets because no one wanted to shake hands.

Rob - I mean this relates to what I think is like one of the biggest mysteries of the Earth. It's on par with the pyramids in Egypt, which is the human armpit. We have these glands in the human armpit called apocrine glands and the only thing they do, and this is very clear is they feed particular microbes. When they feed those microbes, they metabolise the food that our bodies give them. That's what armpit odour comes from. In non-human primates we know that aroma is super important for signaling between individual. Gorillas can tell each other apart by sniffing. It's this whole organ that was very key evolutionarily and that we've now tried to hide in any way that we can.

Chris - That's exactly what was on the tip of my tongue as you were saying that. Why have we evolved then to try and hide it? Why do we go to enormous efforts to mask this stuff? Is that just learned behaviour?

Rob - A big part of it is the pharmaceutical industry, the cream and antiperspirant industry, which sold us on the idea that we need those products. A big part of the globe has a version of these apocrine glands that are sealed shut, it's a single gene difference. This is true in most of China, but the antiperspirant companies have found that they can sell antiperspirant to those people just by convincing them that they might smell. But also I think our armpits betray our emotional status, they betray our health. You might imagine that there's some advantage socially to hiding what's being said there.