Gel nail polish has become the dominant professional manicure format worldwide, prized for a high-gloss, chip-resistant finish that ordinary air-dried lacquer cannot match and for a cure time measured in seconds rather than minutes under a UV or LED lamp. That speed and durability are not incidental — they depend on a photoinitiator that absorbs light energy and triggers the polymer to harden almost instantly. TPO has long been the industry’s photoinitiator of choice for this role, valued for efficient curing, colour stability, and compatibility with a wide range of gel and builder-gel formulations, which is precisely why its regulatory status matters to such a large slice of the nail industry.

Great Britain’s restriction on TPO in gel nail products has been widely reported as a cosmetics story. It is also, quietly, a textbook example of how a single GHS hazard reclassification can ripple into completely unrelated regulatory regimes — including transport classification under the IMDG Code.

What Changed, and When

From 15 August 2026, manufacturers and importers can no longer place new cosmetic products containing trimethylbenzoyl diphenylphosphine oxide (TPO) on the Great Britain market. A second deadline, 14 February 2027, closes the distributor supply chain for existing stock. Professional technicians in Great Britain may, per CTPA guidance developed with Trading Standards, continue using stock already purchased even after that date — a materially softer position than the EU, where no sell-through provision exists and use on clients stopped outright from 1 September 2025. Northern Ireland follows the EU position under the Windsor Framework, meaning TPO has already been prohibited there since September 2025.

The GHS/CLP Pathway Behind the Ban

TPO’s route to prohibition runs entirely through hazard classification, not a standalone nail-industry decision. The substance (CAS 75980-60-8, EC 278-355-8, harmonised entry index 015-203-00-X) was previously classified Repr. 2, H361f — suspected of damaging fertility — and was permitted in professional artificial nail systems up to 5% under Entry 311 of Annex III (restricted substances) to the Cosmetics Regulation. Commission Delegated Regulation (EU) 2024/197 reclassified TPO to Repr. 1B, H360Fd — presumed to damage human fertility and suspected of harming the unborn child, based largely on animal data. That single reclassification was enough: under the Cosmetics Regulation, a Category 1A or 1B CMR classification triggers automatic prohibition unless a specific derogation is granted, so Regulation (EU) 2025/877 deleted Entry 311 outright and moved TPO into Annex II (prohibited substances). No derogation was sought, given the availability of alternative photoinitiators. The UK’s cosmetics regime mirrors this same trigger mechanism.

TPO’s Separate Life as a Dangerous Good

What rarely makes it into consumer coverage is that TPO also carries its own, entirely independent classification under the IMDG Code — and it has nothing to do with reproductive toxicity. For transport, TPO is assigned UN 3077, Class 9 (Miscellaneous), Packing Group III, with EMS F-A, S-F, under the proper shipping name Environmentally Hazardous Substance, Solid, N.O.S. (Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) and carries marine pollutant status. This classification is built entirely on aquatic toxicity data (fish LC50 in the 1–10 mg/L/48h range) — the environmental hazard block of GHS, not the health hazard block that drove the cosmetics ban.