By Natural Selection Fightwear. We build rashguards out of natural fibre, so fabric chemistry is our day job. Every claim below is checked against the published research it links to. Last updated 4 August 2026.
The short answer
If you are wondering why does my rashguard smell even though you wash it, the answer is that your sweat is nearly odourless on its own. Bacteria living on your skin feed on the oil in it and excrete small, smelly molecules. Polyester attracts and holds that oil, so the raw material for the smell survives the wash.
That is the whole chain, and the reason most laundry advice only works for a week.
Sweat doesn't stink. Bacteria eating it does
Fresh sweat is mostly water and salt, and close to odourless when it leaves you. The smell gets made later, by microbes, in three steps.
- You deposit fuel. Sweat carries dissolved solutes, and your skin adds sebum, an oily mix of fatty acids and lipids. Both land in the fabric.
- Bacteria colonise the fabric, transferring off your skin and settling in.
- They metabolise the fuel into odour, breaking long-chain fatty acids and amino acids into much smaller, volatile compounds. Volatile is what "smelly" physically means: light enough to float off the fabric and reach your nose.
Callewaert et al. (2014), in Applied and Environmental Microbiology, collected shirts after a spinning session and named micrococci the main culprit on clothing, "known for their enzymatic potential to transform long-chain fatty acids, hormones, and amino acids into smaller, volatile compounds, which have a typical malodor."
Worth clearing up one confusion: corynebacteria cause much of the classic armpit smell but, per the same study, fail to grow on textiles. So bjj gear smell is not your armpit, transferred. It is a different microbial community living on the garment itself.
Why the smell comes back the moment you warm up
It came out of the wash smelling fine, then five minutes into warm-ups it stinks again. Nothing regrew that fast. The odour compounds were already there, sitting dormant in the fibre. Volatile molecules need energy to leave a surface, and body heat plus moisture supplies it, so residue that survived your wash lifts off within minutes. It came out of the machine cold and dry with the residue still sitting in the fibre.
The bit nobody explains: polyester loves oil, and odour is oily
Polyester is hydrophobic, it repels water. It is also oleophilic, it attracts oils. Those two together are the problem, because what your body deposits is oily and your washing machine runs on water.
Rachel McQueen of the University of Alberta, quoted in Chemistry World, puts it directly: "oily odorous compounds may more selectively absorb onto polyester, making it hard to clean up sweat smells and bacterial waste." A Chemistry & Industry review adds that polyester "will repel the water but attract many of the other oily type compounds that have come from our bodies in the sweat."
Cotton and bamboo viscose do the opposite. They are hydrophilic, drawing water into the fibre itself, so detergent reaches where the soil is.
| Fibre | Water affinity | Oil affinity | What happens in the wash |
|---|---|---|---|
| Polyester (PET) | Repels water | Attracts and holds oil | Wash water is repelled, so oily residue is under-reached and accumulates |
| Cotton | Absorbs water | Holds oil less tightly | Detergent penetrates the fibre, so residue can be lifted out |
| Bamboo viscose | Absorbs water | Holds oil less tightly | Same as cotton: water gets in, so detergent reaches the soil |
That table answers "why does polyester smell worse than cotton." Not because polyester gets dirtier. Because it holds the wrong thing and refuses the solvent you are cleaning it with.
A second finding almost nobody has picked up. Møllebjerg et al. (2021), in Microbiology Spectrum, found "the hydrophobic polyester absorbed more sebum and more sweat solutes compared to cotton," and that the two store it differently: cotton showed "formation of spherical sebum droplets," while in polyester "sebum was much more homogenously distributed. It coated the fibers and spanned the space between fibers." Bacteria in polyester get an evenly spread film. In cotton they get scattered beads. The study measured the consequence too, reporting "higher initial activity in polyester than in cotton."
Micrococci: the group that grows better on synthetics
Callewaert's most quotable line is one sentence: "the micrococci are able to grow better on polyester." Micrococci are the group carrying the enzyme kit for turning fatty acids and amino acids into malodour compounds. So polyester is not just holding more fuel. It hosts more of the specific organism that converts fuel into stink.
What permastank actually is
Permastank (or permastink): accumulated oily odorant residue bound inside the fibre, built up layer on layer over dozens of wear-and-wash cycles, that ordinary washing never fully removed. It is a chemical deposit rather than a live infestation.
That definition explains what confuses everyone. You can kill every bacterium on a garment and it will still smell, because sterilising removes the factory and does nothing about the product already sitting in the fibre.
It also explains the slow slide. A rashguard is not fine and then suddenly ruined. Each session adds oil, each wash removes some but not all, and the remainder compounds. The one that stinks at month eight was loading up from week one.
Why your rashguard smells after washing
Four reasons, each tied to the mechanism above rather than to laundry folklore.
- Cold water under-cleans oil, because sebum is a fat and fats stay stiff when cold. Cold-wash advice protects elastane, but it is a tradeoff sold as a free win.
- Standard detergent is dosed for water-soluble soil, the mud and salt of everyday laundry. Surfactants have to physically reach the oil to lift it, and on a fibre repelling the water that carries them, plenty never arrives.
- Fabric softener makes it worse, because it deposits a waxy film. You seal a layer over residue you failed to remove, and add something else for oil to cling to.
- Too much detergent leaves film, since overdosing does not rinse out fully. The leftover holds soil and gives the next round of odorants somewhere to sit.
What actually works, and what it can't do
Ranked by the mechanism each addresses. If a method does not target oily residue bound in the fibre, it cannot fix permastank, whatever it does to the smell today. That test is why this list disagrees with most guides on how to get smell out of a rashguard.
| Method | What it targets | Realistic result | Cost |
|---|---|---|---|
| Enzyme detergent (with lipase) | The oily residue itself, by breaking down fats | Best available option. Works on the actual problem | Normal detergent price |
| Oxygen bleach presoak (sodium percarbonate) | Odorant molecules, by oxidising them | Strong. McQueen names percarbonate presoaks specifically | Cheap, needs a soak |
| Warm wash instead of cold | Lipid mobility, fats shift more readily when warm | Genuine help, with a genuine cost | Shortens elastane life |
| Prompt drying, ideally in sun | Mildew and damp-bag smell | Effective, but a different problem to permastank | Free |
| Vinegar soak | pH, plus mild acid neutralising | Short-lived. Does not dissolve sebum | Cheap |
| Bicarb soda | pH, plus some odour absorption | Short-lived, same reason | Cheap |
Two of those need saying out loud. Vinegar and bicarb are pH tools, not solvents. Use them if you like, just do not expect a permanent result from a temporary mechanism.
And warm versus cold has no free answer. Every ranking page states cold as gospel and half contradict each other on why. The truthful version: warm cleans better, cold makes the garment live longer, and you are choosing between them. Skip the hot dryer either way. Chemistry World notes researchers also advise against defaulting to high wash temperatures, on environmental grounds.
Australian conditions make this worse
Most guides on this are written for American or European gyms. A bag in a car boot through a Brisbane or Darwin summer is an incubator: warm and damp, the two things that most accelerate bacterial activity. No-gi runs year-round here, so the rashguard is in constant rotation rather than seasonal. Get it out of the bag the same day, always.
The free advantage nobody mentions is line-drying in Australian sun. Fast, thorough, costs nothing, and spares the elastane a dryer cycle.
When a rashguard is done
Permastank is cumulative, so at some point the garment is finished and no product will save it. Three observable signals:
- It smells within minutes of warming up, straight off the drying rack.
- It smells coming out of the dryer, before it touches your skin.
- The smell survives a proper oxygen-bleach presoak.
The third is the real test, because a percarbonate soak is roughly the ceiling of what home laundry can do. If odour survives it, the residue is beyond reach. Retire the rashguard to drilling or bin it. Every other page in these results will point you at one more spray or soak at this stage, and none of them reach residue a percarbonate presoak already failed on.
Where this leaves your training gear
Follow the mechanism to its end and the conclusion is about material, not technique.
If the problem is an oil-loving fibre gripping oily odorants and refusing the water you clean it with, a water-loving fibre starts from a better position. That is why we build our bamboo and cotton rashguards from over 90% natural fibre, 64% bamboo viscose and 28% organic cotton with 8% elastane for stretch. Our fabric is OEKO-TEX Standard 100 certified, Class I.
The honest part. No fabric is odour-proof, and this one still needs washing promptly and drying properly. Natural fibre takes longer to dry than polyester, which is exactly what absorbency costs you. It also needs blending to survive grappling, because pure natural fibre lacks the stretch recovery a skin-tight garment under load demands. That is what the elastane is for, and we would rather name the tradeoff than pretend it away.
More on the material: how natural fibre behaves against sweat, our position on polyester vs natural fibre for grappling, and the routine for washing your training gear.
FAQ
Why does my rashguard still smell after washing it? Odour compounds are oily, and polyester attracts oil while repelling the water your detergent travels in. Each wash removes some residue but not all, and what stays builds up over months.
Does sweat itself smell, or is it the bacteria? Bacteria. Fresh sweat is nearly odourless. Skin bacteria on the fabric break the fatty acids and amino acids in sweat and sebum into small volatile molecules, and those are what you smell.
Does a vinegar soak actually remove rashguard odour, or just mask it? Neither exactly. Vinegar shifts pH and neutralises some acidic compounds, so the improvement is genuine but short-lived. It does not dissolve sebum, so the residue stays in the fibre and the odour returns.
What is permastank and can you get rid of it permanently? Oily odorant residue accumulated inside the fibre over many wash cycles. An enzyme detergent or oxygen-bleach presoak reduces it substantially. Once it survives a proper presoak, the garment is realistically done.
Should I wash my rashguard in hot or cold water? Warm cleans oil better, cold preserves elastane longer. There is no free answer. Warm wash with an enzyme detergent, and skip the hot dryer, since sustained high heat wrecks stretch fastest.
Do natural fibre rashguards smell less than polyester? Natural fibres are hydrophilic, so they hold water and release oils more readily, meaning detergent can reach the residue. No fabric is odour-proof, and natural fibre trades dry time for that absorbency.
How do I stop my gear smelling in humid Australian summers? Heat and damp accelerate bacterial activity, so a bag left in a hot car is the worst case. Take gear out the same day, wash promptly with an enzyme detergent, and line-dry in sunlight rather than using the dryer.