Kojic Acid Just Hit a Ceiling in Europe. The Others Haven't.

Tranexamic acid, alpha arbutin, kojic acid and azelaic acid show up together on brightening-serum shelves so often that they read like one ingredient family, four ways of doing the same job. They are not regulated as one family anywhere. Each currently sits in its own legal position, and the differences say more about how untested claims survive than any side-by-side comparison of the molecules themselves.

A ceiling that only exists in one place

In April 2024 the European Commission adopted Regulation (EU) 2024/996, which caps kojic acid at 1 percent in cosmetic products and alpha arbutin at 2 percent in face creams and 0.5 percent in body lotions, with plain arbutin capped at 7 percent in face creams. The change followed a Scientific Committee on Consumer Safety opinion flagging possible thyroid-related effects from kojic acid at the higher concentrations, often 2 percent, that had been common in brightening formulas, and a separate SCCS finding that arbutin's risk comes not from arbutin itself but from its capacity to release hydroquinone, a substance the EU already restricts. New products containing either ingredient above those limits could not be placed on the EU market after February 1, 2025; existing stock had to clear shelves by November 1, 2025.

No such ceiling exists in the United States. The FDA has not set a kojic acid or arbutin limit for cosmetics; a serum at 2 percent kojic acid that is now illegal to sell new in Paris remains legal to sell in any American drugstore.

Azelaic acid's split identity

Azelaic acid runs the opposite direction. The EU places no concentration limit on it at all. In the United States, it has a harder line, just drawn by drug approval rather than cosmetic law. Finacea, a 15 percent azelaic acid gel, was FDA-approved for rosacea in 2002; Azelex, a 20 percent cream, was approved for acne in 1995. Both require a prescription. Cosmetic azelaic acid sold without one, including widely stocked serums, tops out near 10 percent, a ceiling no regulator wrote down but that the industry holds to in order to stay clear of drug classification. The clinical evidence behind azelaic acid, in other words, was largely generated at concentrations you cannot buy over the counter.

The one with no line drawn anywhere

Tranexamic acid has neither an EU restriction nor an FDA over-the-counter monograph. Its only FDA approvals are oral and injectable, for heavy menstrual bleeding and short-term hemophilia prophylaxis. Its reputation for fading pigmentation traces back to a Japanese clinical observation in the 1970s, in patients taking it for an unrelated condition, not to a topical dosing framework any agency has since formalized. Of the four ingredients, it is the newest to widespread serum use and the one with the least regulatory anchoring, not because it has failed a safety review, but because none has been completed.

Korea's list skips three of the four

South Korea's Ministry of Food and Drug Safety keeps a fixed roster of "notified" whitening ingredients, including niacinamide and arbutin at set concentrations, that qualify a product for a simplified functional-cosmetic approval. Arbutin is on that list. Kojic acid, tranexamic acid and azelaic acid are not, which means a Korean brand making a whitening claim with any of those three must submit its own efficacy data for individual review rather than relying on the fixed formula.

None of this settles which ingredient works best for a given case of pigmentation. It settles something narrower and more checkable: what "clinically studied" or "dermatologist recommended" can mean changes ingredient by ingredient, and a label listing all four together is quietly asking readers to treat unequal evidence as equivalent.

Sources: EUR-Lex, Regulation (EU) 2024/996 · FDA label, Finacea (azelaic acid) gel 15%