What do people get wrong about washing sportswear and its smell?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
With the spread of running and gym-going, the complaint that polyester sportswear "smells even after washing" is shared worldwide. This article works through the fix from the nature of the fibre and what is known about the bacteria behind the smell.
What to base your decision on
| Item | Detail |
|---|---|
| Why it smells | Polyester repels water but readily holds skin oil. Cotton releases skin oil together with the water; polyester keeps it. Bacteria break down the leftover oil and produce the smell |
| Leaving it | Sweat-soaked kit left in a bag or basket for a few hours is the ideal condition for growth. Wash as soon as you get home; if you cannot, spread it out to dry |
| Detergent | A mildly alkaline liquid detergent or a "sportswear" detergent (breaks down skin oil). No fabric softener (its coating worsens absorbency and oil build-up, and seals the smell in) |
| Temperature | Around 40°C (104°F) (check the label; polyurethane/elastane blends are often labelled 30°C or below) |
| Soaking | 30 minutes in lukewarm water with liquid oxygen bleach (酸素系漂白剤, sanso-kei hyōhakuzai) dissolved in it. No chlorine bleach (colour loss, fibre damage) |
| Inside out | Skin oil is on the inside. Turn inside out and use a laundry net |
| Drying | Quick-drying, so a few hours in the shade is enough. A tumble dryer damages stretch fabric (check the label) |
| Anti-odour finishes | "Antibacterial deodorising" finishes wear off gradually with washing (some labels give a guide number of washes) |
- Detergent-maker research shows that bacteria that break down skin oil, such as *Moraxella*, are the main cause of damp-dry smell and sportswear smell (see the article on towels).
- Polyurethane (stretch) blends are degraded by heat and chlorine, so no hot tumble drying and no chlorine bleach (the same as swimwear, see that article).
- A soak in baking soda (重曹, jūsō, mildly alkaline) also works on skin oil, but oxygen bleach is generally described as working on the bacteria as well.
[Verify] The link between polyester's oil retention and bacteria is based on textile science and detergent-maker research. Check the symbols against the Consumer Affairs Agency's "Care labelling" page.
Misunderstanding 1｜Quick-drying fabric does not smell
The water dries but the skin oil stays, and bacteria grow on it. A wash that removes the oil is the key.
Misunderstanding 2｜Cover the smell with fabric softener fragrance
Softener coats the fibres and seals in the oil and the smell. "Do not use on sportswear" is the makers' usual guidance.
Misunderstanding 3｜Keep it in the bag until it goes in the machine
Sealed and wet is the condition bacteria need. Wash as soon as you get home, or spread it out to dry first, then put it in the basket.
Misunderstanding 4｜Hot water removes both bacteria and oil
The label's upper limit is often 30°C or below for polyurethane blends and about 40°C even for polyester; heat degrades the stretch. Stay at the labelled temperature and add oxygen bleach.
Misunderstanding 5｜Once the smell will not come out, the garment is finished
An oxygen-bleach soak resets most of it. If the smell still comes back, oil and bacteria are fixed deep in the fibre, and it is time to replace the item. Prevention (wash at once, no softener) works best.
---
Sources
- Consumer Affairs Agency, "Care labelling (from 20 August 2024)" [消費者庁「洗濯表示（令和6年8月20日以降）」]
https://www.caa.go.jp/policies/policy/representation/household_goods/guide/wash_02.html
- Japan Soap and Detergent Association, "Laundry Q&A (sportswear, damp-dry smell)" [日本石鹸洗剤工業会「洗濯のQ&A」]
https://jsda.org/w/index.html
- Japan Chemical Fibers Association, "Characteristics of synthetic fibres (polyester, polyurethane)" [日本化学繊維協会「合成繊維の特徴」]
https://www.jcfa.gr.jp/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
Follow the care label and the maker's instructions for any garment, shoe or bag. For expensive or sentimental items, ask a specialist cleaner or repairer.
Sources
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