By Ethan Li. Sources are linked where the evidence is discussed. Last updated 30 August 2026.
The short answer
If you are wondering why does my rashguard smell even though you wash it, the short answer is that fresh sweat has little smell on its own. Odour develops when bacteria metabolise components from sweat and sebum in the textile. In a controlled model, polyester took up more sebum than cotton, and the researchers associated that greater availability with higher initial bacterial activity.
The studies behind that answer were conducted on exercise T-shirts and controlled cotton/polyester samples. That makes it reasonable to ask the same question about other close-fitting polyester training layers, including gym clothes, running shirts and compression shirts, but that extension is an inference rather than a result those studies tested.
That is the mechanism. The studies below show why polyester and cotton can smell different. They do not prove that every rashguard, fabric blend or wash cycle behaves the same way.
What actually causes the smell: sweat or bacteria?
Fresh eccrine sweat is mostly water. The smell develops when bacteria metabolise components from sweat and sebum into volatile compounds.
- Sweat and sebum enter the fabric. Sweat carries water and dissolved solutes. Sebum supplies lipids.
- Skin bacteria enter with them. Textiles can retain bacteria transferred during wear.
- Bacterial activity produces odour. The bacteria metabolise sweat and sebum components into volatile compounds that can reach your nose.
Callewaert et al. (2014) collected T-shirts from 26 people after a one-hour spinning session, then incubated them for 28 hours before assessment. In that experiment, the polyester shirts smelled more intense and less pleasant than the cotton shirts. Micrococci were found predominantly on synthetic shirts, and a separate controlled experiment found selective growth of Micrococcus luteus on polyester rather than cotton.
One limit matters. The same paper tested one strain, Corynebacterium jeikeium, which did not grow under its three-day textile experiment. The worn garments developed a microbial mix that differed from the wearers' axillary skin, but the study does not show that all corynebacteria fail on all textiles or that garment odour is completely separate from microbes transferred from your skin.
Why the smell comes back the moment you warm up
If a washed shirt seems fine when dry and smells again once it becomes warm and damp, retained odorants or surviving textile microbes may be involved. Møllebjerg et al. (2021) notes that dried biofilm can retain malodorous compounds and may provide nutrients when new bacteria arrive during later wear. The paper did not test how many minutes it takes for smell to return in a washed garment, so the timing cannot be claimed.
The bit nobody explains: polyester loves oil, and odour is oily
Polyester is hydrophobic. In a controlled cotton-versus-polyester model, it also absorbed more sebum and sweat solutes than cotton.
Textile scientist Rachel McQueen gives the same practical explanation in a 2021 Chemistry & Industry review: polyester repels water but attracts oily compounds from the body, and those compounds can be harder to wash out of polyester than cotton.
The 2021 laboratory model measured cotton and polyester only. It did not test bamboo viscose or the V1's 64/28/8 blend.
| What the 2021 model measured | Cotton | Polyester |
|---|---|---|
| Water uptake | Higher | Lower |
| Sebum and sweat-solute uptake | Lower | Higher |
| Initial collective bacterial activity with artificial sweat-sebum | Lower | Higher |
| Activity after the textiles dried | The polyester-cotton difference was no longer present | The polyester-cotton difference was no longer present |
This helps explain an association. It does not prove that sebum alone causes every case of persistent rashguard odour.
Møllebjerg's team also saw sebum collect as droplets in cotton but spread more evenly across polyester fibres. They proposed that the greater amount and accessibility of sebum in polyester explained the higher initial bacterial activity. That is the authors' hypothesis from a controlled model, not proof of a single cause in worn rashguards. After the textiles dried, the activity difference disappeared. The researchers also could not show a significant difference between dried cotton and polyester in bacteria retained after washing because the results were highly variable.
What did the micrococci result show?
Callewaert's worn-shirt experiment found micrococci predominantly on synthetic garments after the spinning session and 28-hour incubation. Its separate three-day textile experiment found the greatest growth of Micrococcus luteus on polyester and no selective growth on cotton. The authors describe micrococci as capable of converting fatty acids into malodour compounds. That supports a material-microbe link under the tested conditions, not a universal claim about every synthetic garment.
What is permastank?
Permastank (or permastink): persistent odour in a textile that can involve retained odorant compounds and, in some cases, microbes or biofilm that survive laundering.
The cause is not necessarily one thing. Antimicrobial treatment can reduce bacteria without removing odorants already held by a fabric. Washing can remove some soils and microbes without removing all of them. Persistent smell can involve both sides of that problem.
Why your rashguard smells after washing
Drying before washing can make bacteria harder to remove from textile fibres. In Møllebjerg's controlled samples, washing removed fewer bacteria after the textiles had dried than before drying. That occurred in both cotton and polyester, and the dried samples did not show a reliable difference between the two materials.
Polyester can add a second problem. The material took up more sebum in the same study, and McQueen reports that oily odorants can be harder to wash out of polyester than cotton. That makes persistent smell plausible even when a normal wash has removed much of the loose soil.
What actually works, and what it can't do
There is no evidence-backed universal ranking for every rashguard and every fabric blend. A 2025 Chemistry World explainer gives four narrower steps from textile researchers:
- McQueen suggests a laundry presoak containing sodium percarbonate and sodium carbonate when odorants have built up.
- She also suggests washing problem garments sooner after wear.
- Researcher Angie Sherry advises drying in lower-humidity conditions and not leaving wet laundry sitting in the machine.
- Sherry and Jane Scott advise against making higher-temperature washing the default.
Follow the garment's care label. A percarbonate/carbonate presoak is one expert-recommended treatment, not proof that every persistent smell can be removed.
Do hot and humid conditions change the problem?
Humidity can slow drying, leaving moisture available for microbes for longer. The sourced advice is simple: dry the garment fully in a lower-humidity environment when possible, and do not leave it wet in the washing machine. The studies reviewed here do not establish a separate Australian effect.
When should you throw out a rashguard?
There is no published disposal threshold in the sources reviewed here. A percarbonate/carbonate presoak may help with built-up odorants, but failure does not prove that the garment is chemically beyond recovery.
The practical decision is personal. If the smell remains after care-label-compatible cleaning and makes the shirt unpleasant to train in, retiring it may be reasonable. That is a judgement call, not a laboratory cutoff.
Why gym clothes and polyester activewear can smell after washing
The strongest direct evidence here comes from cotton and polyester T-shirts after spinning and from controlled cotton/polyester textile samples. Neither study tested BJJ rashguards, compression fits, bamboo-cotton-elastane blends or the V1 itself.
It is reasonable to infer that fibre interaction with sebum and microbes may matter beyond rashguards in other close-fitting polyester training layers. That includes workout tops, running shirts and compression shirts. It is still an inference. The studies do not tell us how garment fit, knit, blend, wear conditions or laundering would change the result.
That is why we built the V1 Hybrid natural-fibre compression shirt from 92% natural fibre: 64% bamboo viscose, 28% organic cotton and 8% elastane for stretch. It is built to handle contact-sport training, then keep working for running, gym training and everyday wear.
The V1 is 92% natural fibre, not 100%. The remaining 8% is elastane. A hybrid compression shirt still has to survive contact-sport training, so we would rather name the compromise than pretend it away. No claim here means the V1 is odour-proof.
FAQ
Why does my rashguard still smell after washing it? Persistent odour can involve odorant compounds held in the textile and microbes or biofilm that survive laundering. Polyester absorbed more sebum than cotton in a controlled model, while drying made bacteria harder to remove from both textiles.
Does sweat itself smell, or is it the bacteria? Fresh sweat has little smell on its own. Bacteria metabolise components from sweat and sebum into volatile compounds, and the textile can retain both microbes and odorants.
Does a vinegar soak actually remove rashguard odour, or just mask it? The sources reviewed for this article do not establish how well vinegar works on persistent rashguard odour. The current expert advice we could source recommends a presoak containing sodium percarbonate and sodium carbonate instead.
What is permastank and can you get rid of it permanently? Permastank is persistent textile odour involving retained odorants and potentially surviving microbes. A percarbonate/carbonate presoak is one expert-recommended option, but no source here supports a guaranteed permanent fix or a point at which recovery becomes impossible.
Should I wash my rashguard in hot or cold water? Follow the garment's care label. The 2025 expert guidance cited above advises against defaulting to higher-temperature washing. The sources reviewed here do not support one universal temperature for every rashguard blend.
Do natural fibre rash guards smell less than polyester? The direct human evidence shows cotton T-shirts smelled less intense and more pleasant than polyester T-shirts after the tested spinning and incubation conditions. It does not prove the same result for every natural fibre, every rashguard blend or the V1 specifically.
How do I stop my gear smelling in humid Australian summers? Wash problem garments sooner after wear, dry them fully in a lower-humidity environment when possible, and do not leave wet laundry sitting in the machine. The evidence reviewed here supports those general moisture-management steps, not a separate Australia-specific rule.
Why do my gym clothes still smell after washing? Persistent odour can involve odorants held in the textile and microbes or biofilm that survive laundering. In the controlled evidence reviewed here, polyester took up more sebum than cotton, while drying made bacteria harder to remove from both materials.
Why do polyester compression shirts smell? Polyester can hold oily compounds from the body that are harder to wash out than they are from cotton. That mechanism may help explain odour in a close-fitting compression shirt, but the studies reviewed here did not test compression shirts or compression fabrics.