Why Does Polyester Smell? Hint: It's Not You | MARINE|O

We've all done it, pulled a synthetic shirt out of the wash, given it a sniff, and found the smell still there. Polyester has a reputation for holding onto odour in a way cotton and wool just don't. So what's actually going on?

The answer isn't really about sweat. It's about what lives in it.

Sweat doesn't smell, bacteria do

Fresh sweat is almost odourless. The compounds it contains are too large to evaporate and reach your nose.

The smell comes later. Bacteria living on your skin feed on those compounds and break them down into small, volatile molecules and those are what you can smell. Body odour is really a bacterial by-product, not the sweat itself.

Polyester is the perfect home for odour bacteria

Here's where the fabric matters.

Polyester is hydrophobic, it repels water but attracts oils. So instead of absorbing sweat, it lets the moisture and skin oils pool in the tiny spaces between fibres. That turns out to be an ideal environment for odour-causing bacteria to thrive.

A 2014 Ghent University study put this to the test: 26 people handed in shirts after an hour-long spin class, half polyester, half cotton. A trained odour panel rated the polyester shirts as significantly more intense and less pleasant. The reason was in the bacteria, polyester was rich in Micrococcus, a microbe that's especially good at turning sweat into smell. Cotton barely grew any.

Why wool is different

Natural fibres behave the opposite way. Wool is hygroscopic, it actively absorbs moisture, pulling sweat away before bacteria can feast on it. Its scaly, uneven surface also makes it hard for microbes to cling on and multiply.

On top of that, wool can trap odour molecules inside the fibre and release them when it dries out or airs off, which is why a merino layer can be worn for days and freshened up with nothing more than a night on the line.

It's the same reason merino works so well for shorts you wear in the heat. If you want the natural-fibre options, we compared them in our guide to the best plastic-free men's shorts in Australia.

The takeaway

Polyester doesn't smell because it's dirty. It smells because its structure quietly creates the ideal conditions for the bacteria that produce odour, and then holds onto the result.

It's a small thing most people never think about. But once you know why one shirt stinks after a single wear and another stays fresh for days, it's hard to unsee.

Sources

• Callewaert et al. (2014), Microbial Odor Profile of Polyester and Cotton Clothes after a Fitness Session, Applied and Environmental Microbiology
• Waqar et al. (2025), Textile Laundering and Body Odor: A Comprehensive Review
• International Wool Textile Organisation (IWTO)

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