Photoinitiators: the light-responsive starting point of curing
A photoinitiator produces reactive species when it absorbs suitable light, helping start a chemical reaction. In photo-curable nail coatings, it is part of the formulation, while the lamp supplies light. [1][2]
KEY TAKEAWAYS
Starting a reaction
The NailKnowledge source used here is professional education for nail practitioners. NailKnowledge’s glossary describes reactive species including free radicals and ions. These names concern different reaction mechanisms; they should not be collapsed into a claim that every light-curable product works identically. The definition identifies a chemical role, not a performance rating. [1]
TPO: chemical function versus EU cosmetic status
TPO is Trimethylbenzoyl Diphenylphosphine Oxide, CAS 75980-60-8. Regulation 2025/877 prohibits this ingredient in EU cosmetics from 1 September 2025. Its historic use as a photoinitiator does not override that prohibition. [3]
The legal change follows TPO’s classification as toxic for reproduction, CMR category 1B, under the CLP framework (Regulation 1272/2008, amended by Delegated Regulation 2024/197). Article 15 of the Cosmetics Regulation 1223/2009 links these classifications to cosmetic prohibitions unless its exception conditions are met. Regulation 2025/877 records that no exception request was submitted: it removes the former Annex III entry 311, which had allowed up to 5% for professional artificial-nail systems, and adds prohibited entry 1731 in Annex II. The former limit is no longer a permission. [3]
The Commission-services Q&A states that the prohibition covers sales, commercial supply and use on salon clients, including stock purchased before that date; it provides no sell-through or use-up period. This is the services’ explanatory interpretation. A “TPO-free” claim concerns one ingredient and does not establish that a formula is allergy-free, compatible with any lamp or independently safety-tested. [4]
TPO, TPO-L and Irgacure 819 are separate table entries
BASF lists TPO, TPO-L and Irgacure 819 in separate rows with different chemical names. Its industrial-coatings table therefore supports distinguishing those substances; the EU TPO prohibition concerns the named TPO ingredient. The supplier table is spectral and product information, not a list of permitted cosmetic ingredients. [3][5]
A named example and its absorption peaks
BASF’s industrial-coatings reference identifies bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as the chemistry behind Irgacure 819. The table lists absorption peaks at 360, 365 and 405 nm. These are the supplier’s example-specific spectral data, not a wavelength recipe for every nail gel. [5]
An absorption peak is not a complete absorption band, and neither tells us the light dose delivered through a pigmented coating. The final formulation, optical path, lamp output and validated instructions still matter. Industrial photoinitiator data do not establish that a substance is currently permitted in EU cosmetics or that a particular branded gel contains it. [2][6]
Light has a spectrum
UV Gel Explained describes initiators activated by particular wavelengths. The useful connection is between a formulation’s light response and documented light output. A lamp’s electrical power or technology label does not, on its own, state that relationship for a specific coating. [2]
Article Sources
- NailKnowledge — Photoinitiators
Industry educational material
Opening definition paragraphs: radiation-triggered reactive species and use in photocurable coatings.
- NailKnowledge — UV Gel Explained, English v6
Industry educational material
Printed pages 11–12: monomers, oligomers and polymer chains; 13–15: initiation and wavelength-dependent photoactivation; 27–29: hardening versus conversion and unreacted components. Professional education used for qualitative mechanisms only; numerical cure thresholds, catalyst generalisations and clinical or operating advice are excluded. Printed and one-based PDF page numbers match.
- European Commission / EUR-Lex — Commission Regulation (EU) 2025/877 of 12 May 2025
Regulatory source
Recitals 1–7, Article 2 and Annex: TPO (CAS 75980-60-8) is removed from Annex III entry 311 and added to Annex II entry 1731. The cosmetic prohibition applies from 1 September 2025.
Adopted:
- European Commission services — TPO in Nail Products – Questions & Answers
Primary source
Questions 2–4: prohibition of sale, commercial supply and professional client use from 1 September 2025, including earlier stock. The opening disclaimer before Introduction identifies this as the Commission-services explanatory view, not an official Commission position or binding judicial interpretation.
Article date:
- BASF — Protecting what’s around us — Resins and additives for furniture and floor coatings
Manufacturer material
PDF page 23 (printed spread 44–45): Irgacure® TPO, Irgacure® TPO-L and Irgacure® 819 rows, chemical-name and UV/VIS absorption-peaks columns. Historical industrial supplier data, not cosmetic permission or a validated curing schedule for a finished gel/lamp system.
- NASA — Spectroscopy 101 – Light and Matter
Primary source
Waves: wavelength is the distance between successive peaks. The “The Electromagnetic Spectrum” infographic and its accessible description in Light give visible light as 380–780 nm and distinguish it from UV.
Webpage updated:
Written and reviewed with AI assistance using the linked sources. No hands-on product testing or independent specialist review was performed.
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