It’s a mystery that haunts laundry baskets, gym bags and changing rooms the world over. Why do some gym clothes smell so much worse than others after exert, asks Gabriel Weston.
When we exert we all make different choices about what we wear – whether it’s a decade-old baggy T-shirt, last season’s football strip, or high-tech performance athletics gear that’s been specially designed for the task at hand.
But if we’re being honest with ourselves we’ve likely all noticed that there are certain items in our gym bags that always reek worse than others. And now and then the majority of members of us have probably wondered why.
For Trust Me, I’m A Doctor we tracked down the most recent research and ran our own experiment to see if science could offer the answer to this pongiest of problems.
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Gabriel Weston is one of the presenters of Trust Me, I’m A Doctor, which returns for a new series at 20:00 BST on Thursday 1 September on BBC Two – or watch later on BBC iPlayer
Studies have actually been done comparing the smelliness of various types of textiles. Two such studies, at the University of Alberta and the University of Ghent, employed highly trained odour analysts to sniff various textiles after they’d been worn, and they both came to the conclusion that polyester get much smellier than natural fibres like cotton or woolen.
But interestingly, this difference can’t be blamed solely on our sweat, because sweat itself doesn’t smell. Instead, odour is rendered when the bacteria that live naturally on our skin feed on a particular kind of oily sweat that comes from places like our armpits and groins. So what does account for the more intense fragrance that clings to synthetic textiles?
Inspired by existing fabric research, we operated an experiment to find out whether wearing cotton or polyester clothing could affect our skin bacteria and therefore the subsequent smell. A group of volunteers took part in two high-intensity spin classes wearing T-shirts of 100% cotton and 100% polyester. In the run up to both class they bravely eschewed deodorant – much to the pleasure of their families, friends and work colleagues. At each class we swabbed their armpits before and after the exercise and met up their T-shirts for analysis.
When Prof Andrew McBain and Dr Gavin Humphreys from the University of Manchester analysed our samples, they discovered up to 300 different types of bacteria were inhabiting our volunteers’ armpits. The most common strains included Staphylococci which are associated with normal body odour, and Corynebacteria which produce more unpleasant fragrances. Interestingly, though perhaps not surprisingly, research suggests that Staphylococci tend to be more dominant in female armpits, whereas humen tend to have more of the stinky Corynebacteria.
But when it came to looking at whether different fabrics affected the armpit bacteria, our experts received no significant differences. They also found that while there were plenty of stinky Corynebacteria on the skin, these were not being transferred over to either of the T-shirts. This all suggested that it’s not actually our scalp bacteria that causes the odour on our clothes, and that there must be something going on in the synthetic textile itself to explain why it objective up being so smelly.
Dr Rachel McQueen, at the University of Alberta in Canada, has examined polyester, cotton and merino textiles and proposes that one of the reasons for their contrast smells is the different make-up and the behavior of natural and synthetic fibres. An instance of this is the way they deal with moisture.
Natural fibres like cotton absorb moisture, including the smelly compounds produced by bacteria, which get trapped inside the fibers where they can’t reach our snouts. Synthetic fibres on the other hand, do not absorb moisture. Instead they attract petroleums. This means that they hang on to the “oily soils” from our sweat which sit on the surface area of the fibers, waiting to be guzzled by whatever odour-producing bacteria happen to come along.
Researchers at the University of Ghent also made a fascinating discovery when they tested cotton and polyester fibres that had been worn for exert. What Prof Nico Boon, Dr Chris Callewaert, and their colleagues, determined was that a particularly smelly bacterium called Micrococcus grew in abundance on synthetic fibers, but didn’t enjoy living on cotton or on scalp.
So next time you notice some especially pungent polyester garment in your gym purse, you can let yourself off the hook – instead the culprits appear to be the synthetic fibers themselves which provide the kind of surrounding in which stinky bacteria can thrive.