TPO, or trimethylbenzoyl diphenylphosphine oxide, is a photoinitiator that starts the curing reaction in gel polish under a UV or LED lamp, and it has been banned in cosmetics across the EU since 1 September 2025.
Also known as: trimethylbenzoyl diphenylphosphine oxide, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, TPO ban, TPO-free gel
Gel polish hardens because a photoinitiator absorbs light from the lamp and sets off the reaction that links acrylate monomers into a solid film. Trimethylbenzoyl diphenylphosphine oxide (TPO) was the industry's favourite photoinitiator because it cures fast and fully under LED light at 365 to 405 nm.
The European Union classified TPO as a substance that is carcinogenic, mutagenic or toxic to reproduction (CMR), category 1B, on the basis of animal data for reproductive toxicity. Through the 7th CMR Omnibus Regulation it was added to Annex II of the Cosmetics Regulation, the list of prohibited substances, and banned from 1 September 2025 in all 27 member states plus Norway and Switzerland, with no sell-through period (Cosmetics Business; Chemistry World).
Great Britain followed with its own dates. Products containing TPO may not be placed on the GB market after 15 August 2026 and may not be sold through after 14 February 2027 (Scratch). The United States has no equivalent restriction.
Manufacturers have moved to replacement photoinitiators such as TPO-L and BAPO types, and TPO-free is now a standard claim on EU gel. TPO plays no part in air-dry lacquer, which sets by solvent evaporation and contains no photoinitiator. It is also a different substance from TPHP (triphenyl phosphate), a plasticiser that appears on free-from lists for regular polish.