No ingredient is universally good or bad; it depends on what your skin already does. A short list of things to look for beats reading the whole label every time.
If your skin is dry
You are looking for two different jobs done together: something that holds water, and something that stops it leaving. グリセリン (glycerin), BG and ヒアルロン酸Na do the first. スクワラン, シア脂, ワセリン and ceramides — セラミド followed by a letter or number — do the second. A product with only humectants and no occlusive can leave dry skin feeling tight once it dries down.
Check where エタノール sits. High in the list, it works against you.
If your skin is oily or you break out
Texture is mostly decided by the oils and the emollients, so look at what kind they are and how high they sit. Heavy occlusives near the top make a product that will feel greasy on you.
Ingredients frequently used in Japanese products for this: サリチル酸 (salicylic acid), ナイアシンアミド (niacinamide), and グリチルリチン酸2K, an anti-inflammatory that appears in a very large share of Japanese products aimed at irritation and acne. In a quasi-drug these will be declared as 有効成分.
If your skin is sensitive or reactive
The two most common triggers are 香料 (fragrance) and エタノール (ethanol). Both are worth checking the position of rather than just the presence — high in the list means a lot of it.
Essential oils count as fragrance for this purpose even when they are listed under a plant name, and “natural” is not a reassurance here. 無香料 on the front means no fragrance was added for scent, but see what 無添加 and organic claims mean for what that does and does not cover.
Shorter lists genuinely help — not because short lists are better, but because they give you fewer variables when something does react.
If you are avoiding one specific ingredient
Check the list, not the claim on the front. Two things make this harder than it should be in Japan: the Japanese display name often differs from the INCI name you know, and collective names like 香料 or a plant extract can stand for many undisclosed components. If you react to something inside a fragrance blend, the label cannot tell you.
Sun protection
SPF and PA numbers describe protection under an application far heavier than most people use, so treat them as a ceiling. What decides whether you will actually reapply is texture — and texture comes from the filter type. Mineral filters (酸化チタン, 酸化亜鉛) sit on the skin and can cast white; organic filters absorb and generally feel lighter. Japan approves several modern organic filters unavailable elsewhere, which is why Japanese sunscreens have the texture reputation they do.
nemidoes this comparison for you: set your skin type and anything you want to avoid, and it flags them in a product’s list from a barcode scan.