What are the common misunderstandings about booster serums (導入美容液)?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
A "serum you use before your toner" is a product category that grew up in Japan. Visitors often ask why anyone would put something on before the toner (化粧水, keshōsui — the watery lotion applied after washing). This article sets out what the product does and what Japanese law allows it to claim.
Where it fits
| Item | Detail |
|---|---|
| Order of use | Cleanse → booster → toner (化粧水) → serum → milky lotion (乳液) or cream |
| Role (industry convention) | Softens the stratum corneum and helps the following toner "take". Formulated with humectants, ethanol, oils and so on |
| Legal category | Cosmetic (some are quasi-drugs, 医薬部外品 — a Japanese category between cosmetics and medicines). Claims are limited to the 56 permitted items, such as "softens the skin" and "moisturises the skin" |
| Wording on "penetration" | As far as the stratum corneum (JCIA advertising guidelines). "Deep into the skin" or "to the dermis" cannot be said of a cosmetic |
| Essential? | No. An item added by people who feel their toner does not take well, or whose skin is very dry |
| Alternative | Applying toner straight after washing (within 30 seconds) is generally described as making a large difference on its own |
- "Booster", "pre-toner" (プレ化粧水), "first serum" (先行美容液) and "introductory lotion" (導入液) are all names for products in the same position, and none has a legal definition.
- Boosters high in ethanol may be designed to feel refreshing and improve spread through evaporation, and can irritate dry or sensitive skin. Check the top of the ingredient list (see the ingredient list article).
- Wipe-off boosters include an exfoliating element, and some people find daily use drying (see the exfoliation article).
[Verify] Check the 56 items against Yakushoku-hatsu 0721 No. 1, and the handling of "penetration" in the advertising guidelines.
Misunderstanding 1｜A booster carries ingredients deep into the skin
Cosmetic penetration stops at the stratum corneum, booster or not. "Deep into the skin" cannot be used in advertising.
Misunderstanding 2｜Everyone needs a booster
It is "one more item" added to the basic routine (toner → milky lotion). If toner applied straight after washing takes well enough for you, you do not need one.
Misunderstanding 3｜The dearer the booster, the better it works
The permitted claims are the same 56 items at any price. The difference is texture and ingredients. Choosing a price you can keep up is the practical approach.
Misunderstanding 4｜With a booster you can skip the toner
A booster is designed to go before the toner and is not the main moisturiser. If you drop one, drop the booster.
Misunderstanding 5｜A tingle means it is working
That is an irritation reaction. Ethanol or exfoliating ingredients may not suit you. Stop using it; if it continues, see a dermatology clinic (covered by Japanese health insurance).
---
Sources
- Ministry of Health, Labour and Welfare, "Revision of the scope of cosmetic efficacy claims" [化粧品の効能の範囲の改正について] (Yakushoku-hatsu 0721 No. 1)
https://www.mhlw.go.jp/file/06-Seisakujouhou-11120000-Iyakushokuhinkyoku/kesyouhin_hanni_20111.pdf
- Japan Cosmetic Industry Association, "Guidelines for appropriate advertising of cosmetics" [化粧品等の適正広告ガイドライン]
https://www.jcia.org/user/business/advertising
- Japanese Dermatological Association, "Dermatology Q&A: Skincare" [皮膚科Q&A スキンケア]
https://www.dermatol.or.jp/qa/
⚠️ 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.
Sources
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