The "Long-Lasting" Sunscreen Claim That Never Made It to the Label

A sunscreen label promises a number: SPF 50, broad spectrum, water resistant for 80 minutes. What it rarely promises is that the number holds up while you are actually standing in the sun. That gap is the subject of the third installment in a 2015 Cosmetics & Toiletries series by Sebastien Miksa, D. Lutz and C. Guy of HelioScreen, the Creil, France testing lab now operating as WENEOS. Part III proposes a new label claim built on photostability data, and reading it a decade later means asking a claim-reading question the article itself does not: what would it take for a claim like this to actually reach a bottle.

The chemistry behind the proposal is straightforward. Organic UV filters work by absorbing ultraviolet radiation, and that same absorption event is what breaks the filter molecules down over time. A sunscreen can pass its labeled SPF test at time zero and still lose real protective power an hour into a beach day, because the chemistry that makes it work is also the chemistry that wears it out. Part I of the series lays out an in vitro protocol to measure that decay across emulsions, oils, alcohols, lipsticks and powders, and Part II runs it against 107 commercial products, concluding that photostability across the full UVA and UVB spectrum, not only SPF, needs to factor into how safety gets assessed. Part III takes that dataset and asks the next question: if you can measure how much protection a product retains under light, why not put that number on the box.

That is a claim proposal, not a claim. The article never states that any regulator adopted the concept, and the silence since 2015 is itself informative. The closest thing to an existing standard is ISO 24443, the international method for in vitro UVA determination, which does include an irradiation step and a critical wavelength calculation but stops short of authorizing a standalone photostability or long-lasting label claim. In the United States, the FDA's proposed over-the-counter sunscreen monograph, still not finalized as of 2026, sets a broad-spectrum UVA-ratio requirement but includes no validated inter-laboratory photostability test. HelioScreen's proposal was built to fill exactly that space, and the space is still open.

Why a decade of no adoption. The honest answer, based on how photostability testing is discussed in the trade press, is reproducibility. A protocol that works reliably in one lab's hands does not automatically produce the same category or number in another lab, and a claim that regulators cannot audit consistently is a claim they will not codify. That is a mundane, procedural reason, but it is the reason that separates a scientifically sound proposal from an enforceable one, and it explains why SPF, for all its own limitations, remains the claim that made it through: it is the claim that a lab in one country and a lab in another can be made to agree on.

The cost of that gap became concrete this year. In fall 2025, class-action suits were filed against several major sunscreen brands, including L'Oreal's La Roche-Posay Anthelios line, alleging a labeled SPF of 60 tested at 34 in independent lab work, and Edgewell's Hawaiian Tropic, alleging a labeled SPF of 50 tested at 20. Cosmetics & Toiletries covered the filings in its own regulatory pages. Those suits were built on static SPF testing, the same time-zero measurement Part II argues is incomplete on its own. A photostability claim would not necessarily have caught the specific discrepancies alleged in that litigation, since those are framed as initial-value gaps rather than in-use decay, but the underlying complaint in both cases is the same: a number on a label that does not match what a consumer actually gets while wearing the product outdoors.

That is the real value of reading Part III now instead of in 2015. It is not evidence that a better sunscreen claim exists on shelves today. It is evidence of where the current claim, SPF as printed, stops describing the product and starts describing a single moment in a lab. HelioScreen mapped the decay curve past that moment for 107 products and proposed a way to label it. Whether that curve ever reaches a bottle depends less on the chemistry, which the series lays out in detail, than on whether a testing method can survive being run by a second lab in a second country and come back with the same answer.