As of the 1 September 2025, trimethylbenzoyl diphenylphosphine oxidetrimethylbenzoyl diphenylphosphine oxide (TPO) – a chemical ingredient in gel nail polish – was prohibited in cosmetic products in the EU after animal studies suggested it could be toxic to human reproduction.
The move has prompted discussion among users and professionals about the potential risk posed by TPO-containing products and, in countries like the UK where it is not yet banned, whether consumers should avoid them.
But what exactly is TPO and why has it been banned?
What is TPO?
Trimethylbenzoyl diphenylphosphine oxide (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) or TPO is a Norrish Type 1 (alpha-cleavage) photo-initiator – a compound that sparks a reaction when exposed to light.
It is used as a photo-initiator for polymerisation in ‘artificial nail systems’, specifically gel nail products, that are hardened rapidly under a UV or LED lamp to form a glossy finish that lasts much longer than a traditional manicure.
TPO can be used in other products, such as inks and adhesives, especially when rapid curing is needed, but it is widely used in gel nail polish because of its broad UV absorption spectrum and because it tends to lead to less yellowing in cured products.
TPO is also used in products that may be ingested, such as lipstick and lip gloss; used near the eyes, such as eyelash glue; used in children’s makeup; or inhaled, such as perfumes.
Why has it been banned in cosmetic products?
In 2023, the European Commission classified TPO as carcinogenic, mutagenic or reprotoxic (CMR) category 1B (CMR substances are classified as category 1A, category 1B or category 2, depending on the level of evidence of their CMR properties).
The 1B classification indicates that TPO is presumed to be toxic to human reproduction largely based on data from animal studies. (Category 1A CMR substances are when there is human evidence that the substance is toxic to reproduction).
On 12 May 2025, the European Commission published a regulation that stated that, in light of the classification, TPO should no longer be allowed in cosmetic products.
This triggered the inclusion of TPO in Annex II (prohibited substances) of the EU’s cosmetics regulation. This decision was discussed by EU member states, with 25 voting in favour, while one voted against and one abstained.
This is not the first time TPO has been up for scrutiny. In 2014, the Scientific Committee on Consumer Safety (SCCS) concluded that TPO was safe in certain professional UV-cured nail gels up to 5% under specified conditions.
As this predates the new CMR classification this opinion no longer applies.
What does the ban mean?
The EU’s Cosmetics Regulation prohibits the use of substances classified as CMR substances from being used in cosmetic products, unless an exemption has been requested and granted.
It means that from 1 September 2025, manufacturers, importers or distributors can no longer place new products containing TPO on the market and TPO-containing products that were already on the market cannot continue to be supplied for public or professional use.
However, this doesn’t mean a complete ban on gel nail polishes, just those that contain TPO.
Where is it banned?
Currently the ban applies to all 27 member states countries in the EU, as well as Norway and Switzerland. TPO is not banned in the UK or the US, although they may end up following suit.
The Cosmetic, Toiletry and Perfumery Association (CTPA) said a ban in England, Scotland and Wales was expected by 2027.
What does it mean for professionals who use these products?
For professionals, such as nail technicians, who use TPO-containing products in their day-to-day work, the ban means that from 1 September they can no longer used these products. This applies regardless of whether the product was purchased before the cut-off date.
All companies and professionals selling or providing TPO-containing products must discontinue sale, supply and professional use, withdraw remaining stock and seek alternatives that are compliant with the regulations. There are significant reformulation efforts going on across the nail industry to produce TPO-free products.
In a statement, UK-based premium nail company The GelBottle Inc said it was ‘actively transitioning’ all of its products to new TPO-free formulations, with reformulated versions already being manufactured. ‘We expect the entire range to be fully TPO-free ahead [of] the UK regulatory deadline (Sep 2026),’ they added in their statement.
How much TPO is there in gel nail products?
Concentrations of TPO in these nail gels range between 0.5%–5%. Applying a gel nail product to both fingernails and toenails would mean using between 2–4g of gel, which corresponds to a maximum of 200mg TPO in total.
Should users of these products be concerned?
In a statement on the ban, Caroline Rainsford, director of science at the CTPA, said the reason TPO had been banned in cosmetic products in the EU was based on its hazardous properties, meaning how a substance might behave under a ‘worst case’ scenario when our bodies are exposed to very large amounts.
‘This is not how TPO is used in cosmetics,’ she added. ‘The amount of this ingredient used in nail products is over a thousand times less than the amount which could have any negative effect on fertility and these products are applied to the nail, so the potential for the ingredient to be absorbed into our bodies is even smaller.’
‘All these factors are taken into account through the legally-required, robust safety assessment which all cosmetic products must undergo before being sold, by a duly qualified and experienced safety assessor.’
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