What do people get wrong about underarm sweat marks and yellowing?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Yellow underarm stains on shirts are a worldwide complaint, and "is it the antiperspirant or the sweat?" comes up again and again on forums abroad. Here we sort out the causes and how to remove the stains, with Japan's sweaty summers and its antiperspirant habits in mind.
Causes and responses
| Cause | Mechanism | Response |
|---|---|---|
| Oxidised skin oil | Skin oil left after washing yellows over time | Wash straight after wearing; pre-wash the underarms (apply neutral detergent directly and rub gently) |
| Antiperspirant ingredients | Aluminium salts + sweat + skin oil bind to the fibre, causing yellowing and stiffening | Let the antiperspirant dry before dressing, use less, apply at night (only a thin layer in the morning) |
| Apocrine sweat | Sweat from the underarm apocrine glands contains protein and lipids and colours as it oxidises | Sweat pads (the stick-on type for clothing, 汗取りパッド), an undershirt |
| Fibre | Cotton yellows readily; polyester holds odour | Bleach white shirts regularly with oxygen bleach |
Removal
| Stage | Method |
|---|---|
| Light yellowing | Apply liquid oxygen bleach directly, leave 30 minutes → normal wash |
| Set-in yellowing | Dissolve powdered oxygen bleach in water at 40–50°C (104–122°F) and soak for 30 minutes to 2 hours (check the temperature and bleach symbol on the care label) |
| Hardened antiperspirant build-up | Mix powdered oxygen bleach + baking soda (重曹) with a little water into a paste → apply, leave 30 minutes → brush gently → wash |
| Won't come out | Take it to a dry-cleaner and say it is "yellowing" (黄ばみ, kibami). Do not use chlorine bleach (it strips colour from patterned items; even on whites it can discolour the fabric and buttons) |
[Verify] Check the bleach-symbol categories against the Consumer Affairs Agency's "Care labelling" page, and antiperspirant ingredients against the product label. The removal methods are the general guidance of detergent makers.
Misunderstanding 1｜It's the colour of sweat, so stop the sweat
Sweat is almost colourless. The main cause is the reaction between skin oil and antiperspirant. Many people report less yellowing after cutting down on antiperspirant.
Misunderstanding 2｜Chlorine bleach will definitely shift it
Chlorine bleach can react with the aluminium in antiperspirant and cause more yellowing and fabric damage. Oxygen bleach is the rule.
Misunderstanding 3｜More antiperspirant means fewer sweat marks
Too much means more build-up in the fibre, and more yellowing and stiffening. The right amount, and let it dry before you dress. Applying at night works while you sweat less and lets you use less in the morning (see the antiperspirant article).
Misunderstanding 4｜Once it's yellow, bin it
An oxygen-bleach soak fades most of it. The sooner, the easier. A batch soak before the seasonal wardrobe change (衣替え, koromogae) is a standard habit among people living in Japan.
Misunderstanding 5｜Sweat pads are over the top
Stick-on sweat pads are the most reliable prevention for extending a shirt's life, and in Japan they are an everyday item. Undershirts with built-in underarm pads work the same way.
---
Sources
- Consumer Affairs Agency, "Care labelling (from 20 August 2024)", bleach symbols [消費者庁「洗濯表示（令和6年8月20日以降）」漂白記号]
https://www.caa.go.jp/policies/policy/representation/household_goods/guide/wash_02.html
- Japan Soap and Detergent Association, "Types of bleach and how to use them" [日本石鹸洗剤工業会「漂白剤の種類と使い方」]
https://jsda.org/w/index.html
- Ministry of Health, Labour and Welfare, "Scope of permitted claims for quasi-drugs" (antiperspirants; a quasi-drug is a Japanese category between cosmetics and medicines) [厚生労働省「医薬部外品の効能効果の範囲」]
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/iyakuhin/keshouhin/index.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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