What are the common misunderstandings about emulsions and serums?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Japanese skincare has many steps: lotion (化粧水, keshōsui — a watery toner), serum (美容液, biyōeki), emulsion (乳液, nyūeki — a light, milky moisturiser) and cream. Visitors often ask why there are so many stages, and what an "emulsion" actually is. Here we sort the products by their legal category and their role.
Roles (the customary classification)
| Product | Main role | Texture | Legal category |
|---|---|---|---|
| Lotion (化粧水, keshōsui) | Gives water; helps the next product spread | Watery | Cosmetic |
| Serum (美容液, biyōeki) | Adds a higher level of particular ingredients (moisturising or skin-conditioning ingredients, etc.) | Gel to slightly thick | Cosmetic (some are quasi-drugs) |
| Emulsion (乳液, nyūeki) | Adds water and oil, and slows evaporation | Milky (oil-in-water) | Cosmetic |
| Cream | More oil; a firmer lid | Thick | Cosmetic |
- These classes are industry custom and have no legal definition. The Pharmaceuticals and Medical Devices Act (Japan's cosmetics and drugs law) has only three categories: "cosmetics", "quasi-drugs" and "medicines".
- A cosmetic may claim only 56 listed effects ("moisturises the skin", "protects the skin", "keeps the skin healthy", and so on). The same range applies to a serum and to an emulsion. "Erases wrinkles" or "makes dark spots disappear" cannot be claimed.
- A quasi-drug ("medicated", 薬用) serum — a quasi-drug is a Japanese category between cosmetics and medicines — may state approved claims for its approved active ingredient (e.g. niacinamide, tranexamic acid, retinol): "suppresses melanin production and prevents dark spots and freckles", or "makes fine lines caused by dryness less visible (efficacy evaluation test completed)".
[Verify] Check the 56 items against MHLW notice Yakushoku-hatsu 0721 No. 1, and the scope of quasi-drug claims against Ministry of Health, Labour and Welfare (MHLW) materials. "Makes fine lines caused by dryness less visible" is wording based on the Japan Cosmetic Industry Association's efficacy evaluation test guideline.
Misunderstanding 1｜An emulsion is oil, so oily skin does not need one
The oil content of emulsions varies widely between products, and light, fresh types exist. The basic idea in Japanese skincare is that if you add water and put no lid on it, the water evaporates and the skin dries (see our article on oily skin).
Misunderstanding 2｜The more expensive the serum, the better it works
Cosmetic serums all share the same range of permitted claims; the differences are in ingredients and formulation. The quasi-drug label and its active ingredient tell you more than the price does.
Misunderstanding 3｜The more serums you layer, the better
Layering several serums can stack up irritating ingredients, or leave product sitting unabsorbed on the skin. The usual advice is to pick one or two goals.
Misunderstanding 4｜Lotion after emulsion penetrates better
The customary order is from the most watery product to the most oily. Lotion after emulsion means putting water on top of a film of oil. Products the maker has designed as a "pre-emulsion" (先行乳液, senkō nyūeki) are the exception — follow the label.
Misunderstanding 5｜A Western "moisturiser" is the same as an emulsion
A "moisturiser" abroad is closer to emulsion and cream combined; it is not split as finely as in Japan. Replacing "lotion → serum → emulsion" with a single moisturiser can work perfectly well, depending on your skin type.
---
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, 21 July 2011)
https://www.mhlw.go.jp/file/06-Seisakujouhou-11120000-Iyakushokuhinkyoku/kesyouhin_hanni_20111.pdf
- 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]
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/iyakuhin/keshouhin/index.html
- Japan Cosmetic Industry Association, "Guidelines for evaluating cosmetic functions (anti-wrinkle product evaluation)" [化粧品機能評価法ガイドライン（抗シワ製品評価）]
https://www.jcia.org/user/business/
⚠️ 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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