Trimethylbenzoyl Diphenylphosphine Oxide
Nail-builder photoinitiator (often called TPO) under active US Panel review with two related light-stabilizer phosphine oxides; conclusion still open.
Trimethylbenzoyl Diphenylphosphine Oxide is an acylphosphine oxide used mainly as an artificial nail builder. CIR is reviewing it together with two related photoinitiators that the Dictionary lists as light stabilizers: Bis-Trimethylbenzoyl Phenylphosphine Oxide and Ethyl Trimethylbenzoyl Phenylphosphinate.[1]
What it does
In gel and UV-cured nail systems it helps kick off polymerisation when light hits the formula. The two companion ingredients are more often framed as light stabilizers in broader cosmetics.[1]
The evidence
A Draft Tentative Report released 11 September 2026 for the October Panel meeting still has an open conclusion. The Panel has already issued insufficient-data requests covering non-nail use concentrations, skin sensitisation at maximum use, phototoxicity outside nail products, impurities and manufacturing for the two light-stabilizer grades, and related endpoints.[1] Some industry exposure and sensitisation risk assessments have been filed since those requests; several listed gaps remain unchecked in the staff tables.[1]
How to use it
For shoppers, this is a nail-labelling line more often than a face-serum active. Watch for the October Panel outcome before treating any “safe in present practices” claim as settled.