We File One Product Under 'Essence / Ampoule / Serum'. No Regulator Defines Any of the Three.

Search our own catalogue for the word "serum" and three products come back. One is a sunscreen cushion. One is a cleansing oil. One is filed, in our own system, as a mist.

Then there's the fourth bottle. lacelltix Skin Recovery Pepta Tox Ampoule sits in a product category we typed out ourselves, and the category we typed is Essence / Ampoule / Serum. Three nouns, two slashes, one bucket. Nobody made us write it that way. We wrote it that way because we couldn't tell the three apart either.

So we went looking for the rule we were supposed to be following. Korea's type list, Regulation 1223/2009, the FDA codes, the ISO/TC 217 catalogue. None defines any of the three words.

Korea names one of the three words, then walks away

The thirteen Korean cosmetic product types are not where most references still put them. Annex 3 of the Enforcement Rule used to hold the list. It now runs about fifteen lines of general precautions (keep out of reach of children, avoid direct sunlight) and a pointer saying the rest is set by MFDS notice. The type list lives in Annex 1 of 「화장품 사용할 때의 주의사항 및 알레르기 유발성분 표시에 관한 규정」, currently Notice 2026-56, amended 5 August 2026.

The eleventh heading on that list is 기초화장용 제품류, basic skincare, and it has eleven sub-items. In order: astringent, softening and nourishing lotions, which the notice glosses in English as "face lotions"; massage cream; essence and oil; powder; body products; packs and masks; eye-area products; lotions and creams; hand and foot softening products; makeup removers, spelled out as cleansing water, cleansing oil, cleansing lotion and cleansing cream; and everything else.

Item three is 에센스, 오일. Essence, oil. That is the whole treatment — no definition clause, no viscosity band, no minimum active content, nothing that tells a formulator when a bottle stops being a lotion and becomes an essence.

The other two words aren't in the building. We searched Notice 2026-56, the Act, the Decree and the Enforcement Rule for 앰플, 세럼, ampoule and serum. Zero hits in all four. 에센스 appears twice more, as hair essence under type 8 and nail essence under type 9, both bare examples with nothing attached.

Does any of this reach the bottle? It doesn't. Article 10(1) of the Cosmetics Act lists ten things that must be printed on the packaging, and the product type is not among them. Enforcement Rule Article 19(4) delegates eight more, from the barcode to preservative content in products for infants, and the type isn't among those either. The word on the front of a Korean bottle is chosen with total freedom, because it isn't a regulated field.

Brussels wrote a to-do list in 2009 and never finished it

Regulation (EC) No 1223/2009 defines one thing and one thing only: a cosmetic product. Article 2(1)(a) covers any substance placed in contact with the external parts of the body "with a view exclusively or mainly to cleaning them, perfuming them, changing their appearance, protecting them, keeping them in good condition or correcting body odours." Purpose and body site. Not form.

Recital 7 lists what cosmetics "may include" and runs six lines deep: creams, emulsions, lotions, gels and oils for the skin, face masks, bath preparations, depilatories, hair colorants, shaving products, and on. Serum is absent. So is essence. So is ampoule. Recitals are preamble anyway; they bind nobody.

Recital 8 is the one worth reading twice. "The Commission should define the categories of cosmetic products which are relevant for the application of this Regulation." That instruction is seventeen years old and we could not find the act that carried it out. What companies use instead is the category tree in the CPNP User Manual, a three-level dropdown in a 66-page PDF on the Commission's DocsRoom.

Run the three words through the regulation itself and the results are almost comic. Ampoule, zero hits. Serum, one hit, in Annex II entry 323, banning "vaccines, toxins or serums defined as immunological medicinal products." Essence, three hits, all in Annex II, all meaning essential oil in the botanical sense.

Washington is no better organised. 21 CFR 720.4(c) gives thirteen cosmetic product categories, and category 12 is titled "Skin care preparations, (creams, lotions, powder, and sprays)". Four forms, and its ten sub-items aren't forms at all but body sites and jobs: cleansing, face and neck, body and hand, moisturizing, night, paste masks. MoCRA, enacted in December 2022, made product listing mandatory and requires "the applicable cosmetic category or categories" from everyone, then declines to enumerate them. The table filling that gap is FDA's Cosmetics Direct code list, seventeen headings, last revised 11 February 2026. "Serums" appears in it exactly once, at 03(i): "Eyelash and eyebrow preparations (primers, conditioners, serums, fortifiers)." A face serum has no code of its own. It ends up under 14(f) Moisturizing or 14(j) Other.

The only real line anyone draws is a viscosity number

The CPNP form carries a field the category tree doesn't, and this one has a number behind it. Physical form. The manual's note reads: "'Liquid' includes formulations (e.g. solution or milks) with low viscosity, typically below 10.000 cp." Ten thousand centipoise. As far as we can tell that is the only number any regulator has put between a thin skincare product and a thick one, and it exists to sort a dropdown.

Which turns essence-versus-serum into a viscosity question. Does thinner get in better? We expected the permeation literature to say yes, and it says something messier. Stahl and colleagues ran the same 5% ibuprofen through three vehicles in Franz cells under OECD 428, 2 mg/cm², for 28 hours. The cream put 59% of the applied dose into the receptor fluid. The solution managed 26%. The gel managed 21%. The thickest vehicle won by nearly threefold, and the two thin ones left roughly four times more drug sitting in the skin itself. Their conclusion: "it is a mistaken assumption that formulations comprising the same drug amount are equivalent regarding skin permeability."

Bolla and colleagues ran a comparable design on Strat-M membrane and got the ranking inverted. At 24 hours a 3% clear gel delivered 739.6 ± 36.1 µg/cm²; a cream carrying the same 3% in solubilised form delivered 163.2 ± 9.36 µg/cm². Same molecule, same strength, 4.5-fold gap, opposite winner.

Nagelreiter's group went looking for the relationship directly and reported not finding it: "No correlation between formulation viscosity and skin penetration was found." What the base was made of mattered more than how it flowed, and it mattered regardless of how much drug was in it.

What we call our own products

Ours is worse than any of theirs.

Across 54 products we run 54 distinct product types. Every product is its own category, so the field carries no information whatsoever. It's the same defect that surfaced when we checked which of our "cleansers" Korean law actually files as cleansers and found that four of them go somewhere else entirely. Four of those 54 type strings contain one of our three words: Essence / Ampoule / Serum, Ampoule, Hair Essence & Oil, and Body Oil & Essence. None of them is called Serum.

Five product names use one of the three words. Two of the five land in a category that shares it.

Rows two and three are the pair that stings. The Sunday To Monday product is a spicule shot in two 1.4g sachets, one we traced from clinic to shelf earlier this month. Its name contains no ampoule. We filed it under Ampoule. reslow's bottle says Spray Serum and we filed it under Mist. Two opposite mistakes, both ours. Neither breaks a rule. There isn't one to break.

What our screening found

The practical takeaway

In Seoul, Brussels and Washington alike, the noun is packaging copy.

What you can still read off a bottle is the part that is regulated. The full ingredient list is mandatory in all three regimes, printed in descending order down to 1%, and it will tell you in fifteen seconds whether a 50ml "ampoule" is eight peptides deep or three humectants and a fragrance. If the actives you're paying for sit below the preservative system, you're buying a lotion with an expensive name.

Price per millilitre behaves strangely here, because the "ampoule" convention is small volume at high price. We took that apart in the price-per-millilitre piece: a 50ml bottle and a 400ml bottle aren't competing at the same job, and dividing won't tell you which is better.

And if a brand tells you its ampoule is "more concentrated" than its serum, ask what it's more concentrated in. Concentration of what, at what percentage, is a question with an answer. Ampoule versus serum is not.

Our own scoring, which we publish in full, doesn't have a product-type term in it and never did. Given what we found this week, that now looks less like an omission and more like the only defensible option. There is nothing there to weight.