Everything in the product is on the package
Cosmetics sold in Japan must print their complete ingredient list on the package. This has been the rule since a change in the law in 2001, which replaced an older system where only a set of designated ingredients had to be declared. It applies regardless of the size of the manufacturer, so the list you are holding is the full formula, not a selection from it.
On the package this block is labelled 全成分 (zenseibun, “all ingredients”). If you are hunting for it on the back of a bottle, that is the word to look for.
The order tells you roughly how much of each is in there
Ingredients are listed in descending order of quantity. Whatever is first — usually water (水) or a solvent — is the bulk of the product, and things near the top are present in meaningful amounts.
There are two exceptions, and they matter. Anything present at 1% or less can be listed in any order, and colourants are conventionally grouped at the very end regardless of quantity. So you can read the beginning of the list as a ranking, but you cannot compare two ingredients near the bottom and conclude that one is present in a greater amount than the other.
A practical consequence: an active ingredient a product is marketed around, sitting second from last, is present in a trace amount.
The name on the package may not be the name you know
Japanese labels use the display names set by the Japan Cosmetic Industry Association, not the international INCI names used elsewhere. Often the two are close, but sometimes they are unrecognisably different. BG on a Japanese label is butylene glycol. Searching an international ingredient database for the Japanese name frequently returns nothing at all, which makes it easy to conclude a product contains something obscure when it contains something completely ordinary.
If you are trying to look something up and getting nowhere, the problem is usually the name rather than the ingredient.
Quasi-drugs follow different rules
You will see 医薬部外品 (quasi-drug) on a lot of Japanese packaging, often on products marketed for acne, whitening or sun protection. These are a separate legal category from cosmetics, and their labelling rules are different: the approved active ingredients (有効成分) must be declared, but the remaining ingredients (その他の成分) are not covered by the same full-disclosure requirement.
In practice most manufacturers list them anyway, by industry convention — but not always as completely. When you see a label split into two labelled groups, that is what you are looking at, and the second group may not be exhaustive.
Reading it quickly
- The first five or six ingredients tell you most of what the product actually is.
- Collective names hide detail. 香料 means “fragrance” and can stand for a large number of undisclosed components; the same is true of many plant extracts.
- If a name will not resolve in a search, try the INCI equivalent rather than assuming the ingredient is unusual.
- Position matters more than presence. Almost any ingredient can appear in almost any product; where it sits is the information.
For what the recurring ingredients are actually for, see what the common ingredients actually do. If you would rather not do this by hand in a shop, nemi scans the barcode and reads the list for you.