What are the common misunderstandings about patch-testing hair dye?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Home hair colour is convenient, but every year in Japan people report rashes from it, and the Consumer Safety Investigation Commission published a report in 2015. Allergy to the same ingredients (diamines) is an issue abroad as well.
What to consider
| Item | Content |
|---|---|
| Main ingredients responsible | Diamines such as para-phenylenediamine (PPD) in oxidative (permanent) hair dyes |
| Symptoms | A few hours to 48 hours after use: redness, itching and swelling of the scalp, face and neck. Swollen eyelids are characteristic |
| Regulation | Oxidative hair dyes are quasi-drugs (a Japanese category between cosmetics and medicines). A patch test 48 hours before use is stated in the product's precautions |
| Consumer Safety Investigation Commission | October 2015 report on "skin disorders caused by hair dye". Strongly recommended that anyone who has once reacted should stop using it |
| Number of enquiries | Around 200 a year to the National Consumer Affairs Center of Japan (2010s) |
Patch test procedure (example from product labels)
1. 48 hours before use, mix a small amount of solution 1 and solution 2 2. Apply a patch the size of a 10-yen coin (roughly 2 cm across) to the inside of your arm and let it dry naturally 3. Check after 30 minutes and after 48 hours. If there is redness, itching or swelling, do not use the product 4. Do not wash the area during the 48 hours
[Verify] Check the report's date and content against the published documents of the Consumer Affairs Agency's Consumer Safety Investigation Commission, and the enquiry numbers against National Consumer Affairs Center materials.
Misunderstanding 1｜It was fine before, so it will be fine this time
Diamine allergy appears suddenly, once "sensitisation" has built up. Many cases involve people who had used dye for years, so testing every time is what the label asks for.
Misunderstanding 2｜A mild rash just means being a bit more careful next time
Once an allergy has developed, later reactions can be more severe. The Commission recommends that "anyone who has reacted even once should not use diamine hair dyes again".
Misunderstanding 3｜Hair manicure and colour conditioners are the same thing
Acid hair colours ("hair manicure", ヘアマニキュア) and colour conditioners mostly contain no diamines and are classed as cosmetics. They are an option for people with a diamine allergy, but they colour differently, and some people react to other ingredients in them.
Misunderstanding 4｜It is safe at a salon
The ingredients are the same. At a salon too, tell the stylist about any past reaction and ask for a test beforehand if needed.
Misunderstanding 5｜Redness at the hairline is just the dye stinging
Irritation (stinging on the spot) and allergy (swelling hours to two days later) are different things. Symptoms that appear later may be an allergy and need a visit to a dermatology clinic (covered by Japanese health insurance). Swelling of the eyelids or face especially.
---
Sources
- Consumer Affairs Agency, Consumer Safety Investigation Commission, report "Skin disorders caused by hair dye" [毛染めによる皮膚障害] (October 2015)
https://www.caa.go.jp/policies/council/csic/report/
- National Consumer Affairs Center of Japan, "Beware of skin disorders from hair colour" [ヘアカラーによる皮膚障害に注意]
https://www.kokusen.go.jp/
- Japan Hair Color Industry Association, "Safe use of hair colouring: patch tests" [ヘアカラーリングの安全な使い方・パッチテスト]
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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