What are the common misunderstandings about how often to dye grey hair, and which type to choose?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
In Japan, many people from their 40s onwards dye their grey hair regularly, and the drugstore aisle (白髪染め, shiraga-zome) offers a bewildering range. The two common questions are "how often?" and "which type is kindest to hair and scalp?" Here we sort products by their legal category in Japan — quasi-drug (医薬部外品, a category between cosmetics and medicines) or cosmetic — and read this together with our patch-test article.
Types and how to use them
| Type | Category | How it works | Lasts | Typical frequency | Watch out for |
|---|---|---|---|---|---|
| Oxidative hair dye (ヘアカラー / 白髪染め — permanent colour) | Quasi-drug | Colour develops inside the hair. Can also lighten | 2–3 months (regrowth at the roots shows) | Full head: 1.5–2 months; roots: 3–4 weeks | PPD ("diamine") allergy. Patch test 48 hours before every use (see our hair-colour article) |
| Hair manicure (acid hair colourant) | Cosmetic | Colour clings to the surface | 2–4 weeks | 1–2 times a month | Cannot lighten. Stains the scalp and will not come off, so keep a few mm from the skin |
| Colour treatment / colour shampoo | Cosmetic | Builds up colour on the surface little by little | A few days to a week (with continued use) | 1–3 times a week | Gentle colour. Stains hands and towels |
| Henna (plant dye) | Cosmetic (unless it is pure henna, it may contain chemical dyes) | Coats the surface (orange to reddish-brown) | A few weeks | Once a month | Slow (an hour or more). Allergy cases from "henna" containing PPD |
| Temporary colourants (mascara, spray) | Cosmetic | Sits on the surface | Washes out in one shampoo | Each outing | Runs in sweat and rain |
- In its report on skin injuries from hair dye, the Consumer Safety Investigation Commission (2015) recommended that anyone who has once reacted should stop using oxidative dyes and consider products in the cosmetic category.
- The more often you dye, the greater the burden on the scalp. Root touch-ups are less taxing than a full head, and bridging the gap with a colour treatment is an increasingly common approach.
- The causes of grey hair are mainly age and genetics; stress and nutrition play only a partial role. No cosmetic or quasi-drug may claim to "turn grey hair black again."
[Verify] Check the category definitions with the Ministry of Health, Labour and Welfare, and the report with the Consumer Affairs Agency's Consumer Safety Investigation Commission (2015).
Misunderstanding 1｜All grey-hair dyes are the same
Oxidative dyes (quasi-drugs) and cosmetic colourants differ in mechanism, staying power and risk. Choose by whether you have an allergy, and how often you want to dye.
Misunderstanding 2｜Frequency is up to you
Oxidative dyes burden the scalp; the usual guide is full head every 1.5–2 months and roots every 3–4 weeks. Colour treatment in between is the usual approach.
Misunderstanding 3｜No reaction last time means no test needed
PPD allergy can appear suddenly. The product label asks for a patch test 48 hours before every use (see our hair-colour article).
Misunderstanding 4｜Henna is natural, so it is safe
Some products sold as "henna" contain PPD or other chemical dyes, and allergy cases have been reported. Check the full ingredient list. Some people react to henna itself.
Misunderstanding 5｜There are products that turn grey hair black again
No such claim is permitted for cosmetics or quasi-drugs. Claims like "reduces grey hair" or "grows black hair" are problematic under the Pharmaceuticals and Medical Devices Act (Japan's cosmetics and drugs law) and the Act against Unjustifiable Premiums and Misleading Representations (Japan's advertising law). The choice is dye it or leave it.
---
Sources
- Consumer Affairs Agency, Consumer Safety Investigation Commission, report "Skin Injuries from Hair Dye" [毛染めによる皮膚障害] (October 2015)
https://www.caa.go.jp/policies/council/csic/report/
- Ministry of Health, Labour and Welfare, "Scope of Efficacy Claims for Quasi-Drugs" [医薬部外品の効能効果の範囲] (hair dyes)
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/iyakuhin/keshouhin/index.html
- Japan Hair Color Industry Association, "Types of Hair Colour and Safe Use" [ヘアカラーの種類と安全な使い方]
https://www.jhcia.org/
⚠️ 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.
Cosmetics are not medicines and are not meant to diagnose, heal or prevent any condition. If your skin reacts, stop using the product and see a dermatologist.
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