What are the common misunderstandings about washing denim?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
"Never wash your jeans" is advice that has circulated for years in denim-enthusiast communities abroad. In Japan the starting point is different: every garment sold here carries a standardised care label, and a law (the Household Goods Quality Labelling Act) requires it. This article explains what those labels tell you about denim, and where the popular advice goes wrong.
What to base your decision on
- Clothing sold in Japan must, under the Household Goods Quality Labelling Act (家庭用品品質表示法), state the fibre composition, care instructions and the name of the labelling party. Denim is no exception.
- Care labels follow JIS L0001 (Japan's version of the international care symbols; in force since 1 December 2016, revised in August 2024 to 43 symbols). The number inside the wash-tub symbol is the maximum temperature of the wash water. Denim is most often labelled 30 or 40.
- Indigo dye sits on the surface of the fibre rather than inside it, so it comes off easily with friction and heat.
| Item | Guide | Basis |
|---|---|---|
| Wash-water temperature | At or below the number on the label (usually 30–40°C / 86–104°F) | Wash-tub symbol, JIS L0001 |
| Wash inside out | Reduces friction on the outer surface | A common way of limiting friction-related fading |
| Drying | Line-dry in the shade (symbol: a square with a vertical line inside and a diagonal stroke in the top-left corner) | Drying symbols, JIS L0001 |
| How often | When sweat or skin oils have built up | Hygiene; fibres left unwashed for long periods tend to degrade |
[Verify] Check the number of symbols and the dates on the Consumer Affairs Agency's "Care labelling" page, and the labelling obligation on its "Household Goods Quality Labelling Act" page.
Misunderstanding 1｜Denim should never be washed
Sweat and skin oils weaken fibres. Not washing can itself damage the fabric. There are ways to wash less often, but "never" is not something we recommend on hygiene grounds.
Misunderstanding 2｜Putting jeans in the freezer kills the bacteria
This idea spread overseas, but we could find no official evidence that bacteria die at household-freezer temperatures (around −18°C). The smell is only masked for a while.
Misunderstanding 3｜The washing machine is what causes fading
The main causes of fading are the nature of the dye, friction and heat. In a machine, turning the jeans inside out, using a laundry net, cold water and a gentle cycle gets you close to hand-washing conditions. If the label shows a machine-wash symbol, a machine is fine.
Misunderstanding 4｜Colour only bleeds the first time
If wet denim lies against other garments, colour can transfer at any wash, not only the first. Be especially careful with white clothing, synthetic-leather sofas and bags.
Misunderstanding 5｜A hot tumble dryer will shrink stretched jeans back to size
High heat damages the fibres. That is all the more true if the label shows "do not tumble dry" (a circle inside a square, crossed out). We do not recommend the dryer as a way of adjusting size.
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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
- Consumer Affairs Agency, "Household Goods Quality Labelling Act — Textile Goods Quality Labelling Regulations" [消費者庁「家庭用品品質表示法 繊維製品品質表示規程」]
https://www.caa.go.jp/policies/policy/representation/household_goods/guide/fiber/
- Government Public Relations Online, "The new care labels are made up of five basic symbols" [政府広報オンライン「新しい洗濯表示は、5つの基本記号で構成されています」]
https://www.gov-online.go.jp/useful/article/201611/1.html
⚠️ 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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