Perspiration
Sweat itself has almost no smell. What you can smell is bacteria eating it — and which bacteria depends on what the garment is made of.
In detail
The most useful fact about sweat is that it is not the smell. Freshly secreted perspiration has little odour, because the long-chain fatty acids in it are too large to be volatile — a molecule has to be small enough to reach your nose. Bacteria on skin and on the fabric break those acids down into smaller, volatile, strongly-smelling compounds, and that step is the source of the odour. It is why a shirt smells worse after a spell in a bag than it did coming off. Fabric is not a neutral bystander. A study comparing polyester and cotton shirts worn for the same intense session and then incubated found the polyester smelled significantly less pleasant and more intense on every quality the panel assessed. Different bacteria grew: micrococci, which readily break fatty acids into malodour compounds, were enriched almost solely on the synthetics. And the fibres differ: cotton adsorbs volatile molecules well and holds them, polyester adsorbs them poorly and gives them off. Sweat also stains, and that is a separate question from odour. No authoritative account of underarm yellowing has been found for this register, so the odour mechanism is recorded and the staining mechanism is not.
Why
- Perspiration is explained by Classifying a stain by its origin
Sweat is two problems filed as one. The odour is microbial and the fabric changes it; the yellowing is a stain with no sourced mechanism in this register.
Sources for this page
Sources
Microbial Odor Profile of Polyester and Cotton Clothes after a Fitness Session
Applied and Environmental Microbiology, American Society for Microbiology, 2014 · Scientific literature
Relied on for: That fresh sweat has little odour because its long-chain fatty acids are too large to be volatile, that bacteria break these into smaller malodorous molecules, that polyester shirts smelled less pleasant and more intense than cotton after the same session, that Micrococcus was enriched almost solely on synthetics, and that cotton adsorbs volatile odour molecules well while polyester does not. (states this directly)
Verification: a person has read the passage relied on.
Read on — Design, odour-panel results and community fingerprinting. Authors: Callewaert, De Maeseneire, Kerckhof, Verliefde, Van de Wiele, Boon. Supports a narrower statement — our claim was reduced. This supports the mechanism and the fabric difference, and specifically DOES NOT support the thing the intent literally asks — why the smell survives a wash. The paper studied worn and incubated shirts, not laundered ones. CleaningHQ therefore explains why synthetic sportswear smells worse and why sweat itself is not the smell, and records the after-washing part of the question as not answered by this source rather than filling it with the widely repeated claims about detergent residue and fabric softener, which nothing in the register supports.
Last reviewed by a person on .