UV/LED Gel Nail Photoinitiators After the TPO Ban: What 1-Hydroxycyclohexyl Phenyl Ketone Is and Isn't

A UV or LED gel nail polish does not harden on its own. It cures because it contains a photoinitiator: a molecule that absorbs light at a specific wavelength, splits into reactive fragments, and starts the free-radical reaction that turns liquid monomer into a solid film. Without a photoinitiator, a gel under a lamp stays wet indefinitely. Get the photoinitiator wrong, or ban the one a formula was built around, and the whole product has to change.

That is exactly what happened to the nail sector in 2025. Trimethylbenzoyl Diphenylphosphine Oxide (TPO), one of the most widely used photoinitiators in gel systems, was prohibited in EU cosmetic products. This article explains what changed, why, and what is currently known — and not known — about the substances formulators are now searching for as replacements, above all 1-hydroxycyclohexyl phenyl ketone.

What a photoinitiator actually does in a nail gel

Gel nail products are built from acrylate or methacrylate oligomers and monomers that need to polymerise into a hard film. A photoinitiator is the component that makes that polymerisation start on demand, when the product is exposed to a UV or LED lamp, rather than reacting slowly in the bottle. Type I photoinitiators such as TPO and 1-hydroxycyclohexyl phenyl ketone work by direct photofragmentation: absorbed light cleaves the molecule into free radicals, and those radicals trigger the polymer chain reaction. The choice of photoinitiator, and its concentration, determines how fast a gel cures, under which lamp type, and how much unreacted material is left at the surface as uncured, potentially sensitising residue.

The TPO prohibition: what the rule says

TPO (CAS 75980-60-8, EC 278-355-8) is listed in the EU Cosmetics Regulation's Annex II — the list of substances prohibited in cosmetic products — as entry 1731, added by Commission Regulation (EU) 2025/877. Cosingchecker's own record for this entry confirms the CAS and EC numbers and cites (EU) 2025/877 as the amending act.

Before 2025/877, TPO was not banned outright. It had a separate, older entry in Annex III (the restricted-substances list), entry 311, which permitted it in artificial nail systems for professional use only, up to a set concentration. Regulation (EU) 2025/877 deleted that Annex III allowance and moved TPO into Annex II instead, which is why cosingchecker's entries endpoint now returns no Annex III record for CAS 75980-60-8: the professional-use exemption no longer exists in the EU inventory.

The trigger was TPO's classification, under the CLP Regulation (Regulation (EC) No 1272/2008), as a substance toxic to reproduction. Article 15 of the Cosmetics Regulation makes such a CLP classification automatically prohibit the substance in cosmetic products, unless the European Commission has granted a specific derogation — which it did not for TPO. Reporting from industry compliance sources (Pharmilab, GCRS, coslaw.eu) places the application date at 1 September 2025, with no sell-through period for stock already on the market or in salons. A brand or salon still holding TPO-containing product after that date is holding a prohibited product, not a legacy-compliant one.

What replaced TPO, and what its status actually is

Searches for "1-hydroxycyclohexyl phenyl ketone", "hydroxycyclohexyl phenyl ketone" and "cyclohexyl phenyl ketone" spiked after the TPO ban, because it is one of the photoinitiators formulators reach for as an alternative. Cosingchecker's inventory record for this substance (INCI: Hydroxycyclohexyl Phenyl Ketone, CAS 947-19-3, EC 213-426-9, chemical name (1-Hydroxycyclohexyl)phenylmethanone) lists its function in the EU cosmetic ingredient database as Binding — the CosIng function classification, not a description of its actual use as a photoinitiator. The database's function tags describe what CosIng assigns, not the manufacturer's technical use case.

Two things matter for anyone checking this substance's regulatory status. First, cosingchecker's own EU Annex II/III/IV/V/VI query for CAS 947-19-3 returns zero entries: there is no EU annex restriction or prohibition record at this CAS number in the site's data. Second, the ingredient's own record shows zero jurisdiction rules and zero annex-evidence records — meaning that, as far as this database currently shows, the substance carries no annex listing anywhere it tracks. That absence is a statement about the data, not a safety verdict: an ingredient with no annex entry has not been evaluated and cleared, it simply has no prohibition or restriction on file.

The classification picture is also unsettled, and worth checking before repeating anyone's claim as fact. IGM Resins, the lead REACH registrant for the substance (marketed as Omnirad 184), stated in company announcements that new in vivo genotoxicity testing led it to self-classify the substance as Reproductive Toxicity Category 1B, effective from 29 August 2025. IGM Resins subsequently stated it was withdrawing that reclassification because of differing expert interpretations of the underlying data, and that the classification would revert, at least temporarily, to what it was before 29 August 2025, pending independent review. That sequence is significant for two reasons: it was a self-classification by the registrant under REACH/CLP, not a harmonised entry added to Annex VI of the CLP Regulation by the European Commission; and it was itself reversed within days. Anyone relying on "Repr. 1B" for this substance should check ECHA's C&L Inventory and the current Table 3 to Annex VI of CLP directly for the live status, since self-classifications by registrants can change without a corresponding EU Cosmetics Regulation annex entry ever being created.

Other photoinitiators people ask about: TPO-L

Ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate, commonly called TPO-L (CAS 84434-11-7), is chemically related to TPO but is a different substance with a different CAS number. Cosingchecker's entries endpoint returns zero EU annex records for this CAS number, the same absence-of-restriction pattern as for hydroxycyclohexyl phenyl ketone. Some nail-industry blogs describe TPO-L as unaffected by the TPO ban; that claim is plausible given the different CAS number and the absence of any TPO-L-specific EU annex entry, but it has not been verified here against a primary CLP or ECHA classification source, so it should be checked against ECHA's C&L Inventory rather than taken from a secondary blog.

Why "TPO-free" is not the same as "cleared"

A product marketed as "TPO-free" is only telling you which molecule was removed. It says nothing about what replaced it, and a replacement photoinitiator is not automatically lower-risk just because it lacks an Annex II entry today. Annex II and Annex III are populated when the Commission acts, usually after a CLP classification exists — which means a substance can be in wide commercial use, with no annex entry, for years before (or instead of) ever being added. The IGM Resins episode above is a live example of how fast a classification can move, self-classifications included.

• Check the CAS number, not just the marketing name or the INCI name printed on packaging; TPO, TPO-L and hydroxycyclohexyl phenyl ketone are distinct substances with distinct CAS numbers.
• Look up that CAS number against the current EU Annex II and Annex III text (cosingchecker.com/annex/II/) rather than trusting a supplier's compliance statement at face value.
• Check ECHA's own C&L Inventory and Annex VI CLP table for the substance's current harmonised classification; self-classifications by registrants can be provisional and can be withdrawn, as happened with hydroxycyclohexyl phenyl ketone in August 2025.
• For any CMR classification, treat it against Article 15 of the Cosmetics Regulation: a CLP classification as CMR 1A, 1B or 2 triggers an automatic cosmetics prohibition or restriction unless a specific, published derogation exists — check cosingchecker.com/cmr/ for CMR-flagged annex records rather than assuming a classification alone tells you the cosmetics-law outcome.
• For GB-market products, check the GB annex separately from the EU one: GB and EU diverged after Brexit and now update on different schedules.

The GB position: two parallel tracks

Great Britain runs its own, separately amended, Cosmetics Regulation. TPO was added to the GB Annex II as entry 1745 by Statutory Instrument SI 2026/23, which cosingchecker's jurisdiction data records as effective from 15 August 2026 (with sell-through to 14 February 2027, per SI reporting from Cosmeservice and Professional Beauty) — a materially later date than the EU's 1 September 2025 prohibition, and with a sell-through window the EU rule did not grant.

More notably, cosingchecker's GB jurisdiction data still shows a live GB Annex III entry 311 for this substance, with status "restricted". Both GB records carry the date 2026-08-15, which is when the importer captured the consolidated GB annexes rather than when entry 311 took effect. What matters is the text: SI 2026/23 added the Annex II prohibition without removing the older Annex III restricted-use entry from the GB text, unlike the EU regulation, which deleted the equivalent Annex III entry when it added the Annex II ban. Whether that is a drafting gap in the SI, a sequencing issue awaiting a further instrument, or intentional, is not something this database can settle; readers who need a legally reliable answer for a GB-market product should read SI 2026/23 and the current consolidated GB Annex III text on legislation.gov.uk directly, since a database of prohibitions and restrictions is evidence of what is on file, not a substitute for the primary legal text or for professional regulatory advice.

Sources

• Cosingchecker EU Annex II entry 1731 (TPO) record — https://cosingchecker.com/annex/ii/ii-1731-diphenyl246-trimethylbenzoylphosphine-oxide-inci-trimethylbenzoyl-diphenylphosphine-oxide/
• Cosingchecker ingredient record: Hydroxycyclohexyl Phenyl Ketone — https://cosingchecker.com/ingredients/56792-hydroxycyclohexyl-phenyl-ketone/
• Cosingchecker CMR substances hub — https://cosingchecker.com/cmr/
• Cosingchecker EU Annex II hub — https://cosingchecker.com/annex/II/
• Commission Regulation (EU) 2025/877 (EUR-Lex, Official Journal) — https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=OJ%3AL_202500877
• European Commission, TPO in Nail Products - Questions & Answers — https://single-market-economy.ec.europa.eu/sectors/cosmetics/tpo-nail-products-questions-answers_en
• Pharmilab, Prohibition of the TPO ingredient in cosmetics: what changes from September 1, 2025? — https://pharmilab.com/en/2025/07/23/prohibition-of-tpo-ingredient-in-cosmetic-which-changes-from-1-september-2025/
• coslaw.eu, Use of TPO in nail products in the EU — https://coslaw.eu/ingredients-in-the-spotlight-tpo/
• GCRS, Regulation (EU) 2025/877: Nail Ingredient Ban and Brand Impact — https://www.gcrs.co.uk/eu-ban-cmr-nail-products-2025/
• IGM Resins, Statement Regarding Reclassification of 1-Hydroxycyclohexyl phenyl ketone and Ongoing Independent Reviews — https://www.igmresins.com/en/news-events/Statement_Regarding_Reclassification
• IGM Resins, Reclassification of Omnirad 184 and Path Forward — https://www.igmresins.com/en/news-events/Reclassification_of_Omnirad_184_and_Path_Forward
• UK Statutory Instrument 2026 No. 23 (legislation.gov.uk) — https://www.legislation.gov.uk/uksi/2026/23/pdfs/uksi_20260023_en.pdf
• Cosmeservice, UK Cosmetic Regulation SI 2026/23: CMR Bans — https://cosmeservice.com/news/uk-cosmetic-regulation-update-si-2026-23-and-new-cmr-restrictions/
• Professional Beauty, New UK cosmetics regulations 2026: what the July and August changes mean for salons — https://professionalbeauty.co.uk/uk-cosmetics-regulation-changes-2026-salons
• ECHA C&L Inventory / Annex VI to CLP (for readers verifying current harmonised classifications) — https://echa.europa.eu/information-on-chemicals/annex-vi-to-clp