When
we exercise we sweat to keep ourselves cool. Some sweat is produced by eccrine glands found all over the body, but
an oilier kind of sweat is produced by apocrine glands found in places like the armpits. None of
this sweat actually smells, but when specific bacteria living
naturally on our skin feed on the fats and proteins in our apocrine
sweat, they produce an odour which in some cases seems to permanently
infiltrate our gym clothes.
A small survey showed that natural fibres like cotton tend to absorb liquids into the fibre structure so soak up more sweat, while synthetic fibres tend not to so feel drier but does smell worse than cotton after wear.
Researchers found up to 300
different types of bacteria in the armpits of our volunteers, including Corynebacteria which are known to produce
unpleasant smells. There was no significant differences in the armpits when people wore
different fibres, implying that after just one gym session,
the fabric we wear doesn’t affect the bacteria actually on our skin and the Cornynebacteria weren’t among those being
transferred at all, to any fabric.
The problem seems to lie in the fabric itself. Other research has found that polyester retains more odour, and this odour tends to increase over time. Cotton is absorbent, so the odorous compounds produced by bacteria (such as carboxylic acid) are trapped inside the fibres where we can’t smell them. Polyester fibres don’t absorb moisture, but do attract oils, so while the moisture from our sweat evaporates, the ‘oily soils’ cling to the surface of the fibres, where bacteria can transform them into odour.
Research has also found that a bacterium called Micrococcus (known for its odour producing abilities) seems to love growing on synthetic fibres, but didn’t really appear on cotton or on skin. Having tried growing this bacterium on different fabrics, it was found that it did well on polyester. So these bacteria may be the main cause of our smelly synthetic gym clothes.
So it depends on what you care most about: keeping dry or smelling fresh. Cotton minimises smells, but can feel uncomfortable when you sweat. The best solution is probably to wear synthetic clothes and wash them often to prevent the bacteria from multiplying on them.
Should I wear sports clothes from natural or synthetic fabric? BBC 2 Trust Me, I'm a Doctor, Series 5, Episode 1 (1 Sep. 2016)
