INTERNATIONAL CONGRESS OF
PharmacoGenetics
Trimethylbenzoyl Diphenylphosphine Oxide (TPO) in Gel Nail Polishes: A Comprehensive Review
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MehrAra Akanchi,1,* Danial Mirhosseini Vakili,2 Mohammad mahdi Akanchi,3
1. Islamic Azad University of Medical science, Tehran, Iran
2. Islamic Azad University of Medical science, Tehran, Iran
3. Gilan medical university, Iran
- Introduction: Trimethylbenzoyl Diphenylphosphine Oxide (TPO) is a photoinitiator extensively used in gel nail polish and UV-cured nail systems for its efficient radical generation, faster cure under LED/UV light, and reduced yellowing compared to some other photoinitiators. It has been used typically at concentrations up to ~5% in professional gel nail applications. [Reference 1; Reference 4]
- Methods: Literature search was conducted using databases including PubMed, Scopus, Web of Science, and regulatory agency reports (notably EU SCCS opinions) up to 2025, with keywords “TPO”, “Trimethylbenzoyl Diphenylphosphine Oxide”, “gel nail polish”, “photoinitiator toxicity”, “reproductive toxicity”, “CLP regulation”, “cosmetic ban”. Both in vitro and in vivo studies, plus regulatory documents, were included. Exclusion criteria were non-English language, insufficient methodology detail, or irrelevant photoinitiators. [Reference 4]
- Results: The chemical and physical properties of TPO show it is a mono-acyl phosphine oxide, MW ~348.4 g/mol, log P ~3-4, sparingly soluble in water, quickly consumed in photopolymerization, with residual unreacted amounts (if any) assumed low (<<1%) post‐curing. [Reference 4] Toxicity studies in animals indicate testicular atrophy and reduced fertility in repeated dose oral exposure at relatively high doses; skin irritation and moderate sensitization have been documented in dermal or ocular exposure settings. [Reference 4] Genotoxicity assays in vitro (bacterial mutation assays, hprt locus mutation, clastogenicity) showed no significant genotoxic effects under GLP conditions. [Reference 4] Based on such data, the EU has classified TPO as a reproductive toxicant (CMR 1B) and banned it in cosmetic products for nails effective from September 1, 2025. [Reference 3; Reference 6; Reference 0search4]
- Conclusion: Residual TPO after curing is expected to be low and largely trapped in polymer matrix, reducing systemic exposure, but skin and nail-fold contact or occupational exposure can increase risk.
- Keywords: TPO; photoinitiator; gel nail polish; reproductive toxicity; EU regulation; in vitro genotoxicity;
