You have probably seen the phrases ‘HEMA-free’ or ‘TPO-free’ on a gel polish product page and moved on without a clear sense of what either means. That is not a gap in your knowledge — it is a gap in most brand communications. These terms appear everywhere, explained almost nowhere.
This article is the plain-English version. It covers what acrylates are, why HEMA became a concern, what HEMA-free formulas actually contain, why TPO was banned, what the UK’s regulatory picture looks like, and how to read a gel polish ingredient list without needing a chemistry background. By the end, you will have the context to make sense of the claims being made on the products you use.
Acrylates are a family of chemicals, specifically monomers and oligomers, that undergo a process called polymerisation when exposed to UV or LED light. Polymerisation is the moment when individual molecules link together to form a hard, solid structure. In the context of gel polish, that is the curing reaction: the moment your nails go from wet and flexible to hard and glossy under the lamp.
Without acrylates, gel polish as a product does not work. They are not an additive or a preservative; they are the core chemistry. The long-wearing, chip-resistant finish that distinguishes gel polish from ordinary lacquer is entirely a product of the acrylate curing process.
Different acrylates perform different functions within a formula. Some handle adhesion — helping the gel bond to the nail plate so it does not lift. Others affect the flexibility of the cured product. Others still are photoinitiators: chemicals whose job is to absorb light from the lamp and trigger the polymerisation reaction in the first place. Most gel polish formulas contain several acrylates working in combination.
The reason certain acrylates have attracted attention in recent years is not that they are exotic or uniquely dangerous — it is that repeated skin contact with uncured acrylates can, over time, cause sensitisation. Understanding what sensitisation means, and which specific ingredients are involved, is what the rest of this article is about.
HEMA stands for hydroxyethyl methacrylate. It is a small-molecule monomer that has been used in gel nail products for decades because of two properties that made it genuinely useful: it helps the formula adhere to the nail plate, and it keeps the cured gel flexible enough to move with the nail rather than crack.
It is also one of the most thoroughly documented contact allergens in the nail industry.
The mechanism is called sensitisation, a process by which the immune system, after repeated exposure to a substance, learns to react to it. Sensitisation does not usually happen on first contact. Most people use gel polish for months or years without any issue. The reaction appears to come from nowhere, which is exactly how sensitisation works: cumulative exposure crosses a threshold, and the immune system responds. Once that threshold is crossed, further exposures tend to produce a stronger reaction, not a weaker one.
The key variable is skin contact with uncured gel. HEMA that has fully polymerised, properly cured gel sitting on the nail, presents a much lower risk. The problem arises when uncured product repeatedly contacts the surrounding skin: flooding the cuticle area during application, peeling cured gel off instead of soaking it, or, for nail technicians, repeated unprotected contact across many clients over time.
Acrylate sensitisation does not stay confined to nail products. Once developed, it can cross-react with other materials that contain similar chemistry, dental acrylics, certain medical adhesives, some surgical glues. This is why the British Association of Dermatologists (BAD) flags it as a significant health concern, both for consumers and as an occupational issue for nail technicians. The UK’s Office for Product Safety and Standards (OPSS) launched a formal investigation into gel nail products and acrylate allergies in April 2023, following years of growing caseloads at dermatology clinics. Here’s a piece we wrote on gel polish allergies and how to avoid them.
The risk from gel polish is real but it is also specific. Applied correctly, with care taken to keep uncured product off the skin, the risk of sensitisation is low. The issue is not the product itself — it is the conditions under which it contacts skin.
HEMA-free means a formula does not contain HEMA. It does not mean the formula contains no acrylates. That distinction matters because some marketing around HEMA-free products implies a more fundamental safety reassurance than the formulation actually delivers.
The most common alternative to HEMA in HEMA-free formulas is Di-HEMA TMDDM (di-HEMA trimethylhexyl dicarbamate). The key difference is molecular size: Di-HEMA TMDDM is a larger molecule than HEMA, and larger molecules are thought to penetrate skin less readily. That reduced skin penetration is the basis for its lower sensitisation risk profile. But it is still an acrylate, and it can still cause sensitisation in people who are susceptible. HEMA-free is meaningfully safer for most users — it is not a guarantee.
A separate ingredient worth knowing about is IBOA (isobornyl acrylate). Some earlier HEMA-free reformulations used IBOA as a substitute — it was seen as a viable lower-risk alternative. It subsequently emerged that IBOA is itself a sensitiser. Some formulas on the market still contain it. If you have sensitive skin or have had any reaction to gel products, it is worth checking for IBOA specifically on the ingredient list.
The practical position: HEMA-free formulas are the better choice for most people, and the clear choice for anyone who has already shown any signs of sensitivity. Correct application technique still matters regardless of the formula, keeping uncured product off the skin, using proper soaking removal rather than picking or peeling. Our full range of professional Gel polish can be found here.
TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) is a photoinitiator. Its function within a gel polish formula is to absorb light from the UV or LED lamp and trigger the curing reaction. It has nothing to do with colour, flexibility, or adhesion — it is the chemical that makes the lamp work.
TPO was identified as a skin sensitiser and subsequently banned in leave-on cosmetics under EU Cosmetics Regulation. Gel nail polish is classified as a leave-on cosmetic because, once cured, it stays on the nail rather than being rinsed off. The UK introduced equivalent guidance following Brexit.
The practical consequence was a wave of reformulation across the industry. Brands removed TPO from their base coats, colour gels, and top coats, replacing it with alternative photoinitiators — primarily BAPO (bis(acyl)phosphine oxide) and phenylbis — which are considered to carry a lower sensitisation risk. The gel still cures; the triggering mechanism uses different chemistry.
This is the origin of ‘TPO-free’ appearing on product pages. It is a direct response to regulatory change, not a voluntary marketing decision. For most brands, the reformulation occurred across 2024 and into 2025 to meet EU compliance timelines. Older product stock may still contain TPO — if this is a concern, checking the ingredient list is worth the thirty seconds it takes.
In April 2023, the Office for Product Safety and Standards launched a formal investigation into gel nail products in the UK. The trigger was the accumulation of clinical evidence — growing numbers of patients presenting at dermatology clinics with acrylate allergies, including cases of cross-reactivity with dental and medical products.
The investigation examined product labelling, ingredient safety, and whether existing UK cosmetics regulation provided adequate consumer protection. At the time of writing, it has not resulted in a formal ban or mandatory reformulation requirement — but it has raised the floor across the industry. The combination of OPSS scrutiny and EU TPO regulation has pushed most responsible UK brands to reformulate. Products on sale now, from brands that take compliance seriously, are materially different from what was standard five years ago.
The British Association of Dermatologists has published patient-facing guidance on acrylate allergy from gel nail products, as well as guidance for GPs — relevant because acrylate patch testing requires referral to a dermatologist, and general practitioners are not always familiar with the presentation. If you have had any reaction to gel products, asking your GP specifically about acrylate patch testing is the right next step.
The single biggest risk factor for developing an acrylate allergy is not which formula you use — it is how much uncured gel contacts your skin, and how often. This applies to HEMA-free formulas as much as any other.
The practices that meaningfully reduce risk:
For nail technicians, the risk calculus is different because exposure is cumulative across many clients. Gloves are not optional — they are the standard. Proper ventilation and, where clinically indicated, regular patch testing are also part of professional practice. The OPSS investigation specifically highlighted occupational exposure as a significant risk factor.
If you have had any skin reaction — itching, redness, or a rash around the nails following gel polish application — stop using gel products and speak to your GP. Mention acrylate allergy specifically. Continued exposure after the first reaction is when sensitisation typically becomes more severe. Here’s how users can repair their nails after gel polish treatments. And here is a gel polish designed specifically for sensitive or damaged nails.
Gel polish sold in the UK and EU is required to list ingredients using INCI (International Nomenclature of Cosmetic Ingredients) names. These are standardised but not always intuitive. The INCI name for HEMA does not say ‘HEMA’ anywhere. The table below is a quick reference for the ingredients covered in this article.
| INCI name | What it is | Notes |
| Hydroxyethyl Methacrylate | HEMA | The main ingredient to check for — present in non-HEMA-free formulas |
| Di-HEMA Trimethylhexyl Dicarbamate | Di-HEMA TMDDM | Common HEMA alternative in HEMA-free formulas — still an acrylate |
| Isobornyl Acrylate | IBOA | Used as a HEMA substitute in some formulas — itself identified as a sensitiser |
| Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide | TPO | Photoinitiator subject to EU ban — check older stock |
| Bis(acyl)phosphine oxide | BAPO | Common TPO replacement photoinitiator — considered lower risk |
Not all brands list ingredients clearly on their websites, and online product pages sometimes omit the full list. If you cannot find an ingredient list, the physical packaging is the reference point — UK and EU law requires it to be there. For brands that only sell online without a clear INCI list published, contacting them directly is a reasonable ask.
What is HEMA in gel polish?
HEMA (hydroxyethyl methacrylate) is a chemical monomer used in gel polish formulas to help the product adhere to the nail plate and stay flexible after curing. It is effective, but it is also a known skin sensitiser. Repeated contact with uncured gel on skin can cause an allergic reaction that worsens with each subsequent exposure.
Is HEMA-free gel polish safer?
Generally, yes, particularly for people who have shown any sensitivity to gel products. HEMA-free formulas replace HEMA with larger molecules, typically Di-HEMA TMDDM, that are thought to penetrate skin less readily. They still contain acrylates, so they are not allergy-proof — but for most people, they carry a lower risk of sensitisation.
What does TPO-free mean in nail polish?
TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) is a photoinitiator — the chemical that triggers the curing reaction when the lamp is used. It was banned in leave-on cosmetics under EU Cosmetics Regulation because of sensitisation concerns. TPO-free formulas use alternative photoinitiators such as BAPO, which are considered to carry a lower risk.
Can gel polish cause an allergic reaction?
Yes. The acrylate chemicals in gel polish can cause contact dermatitis and sensitisation, particularly when uncured gel repeatedly contacts the skin around the nails. Symptoms include itching, redness, and rash in the nail area. The reaction typically worsens with each exposure rather than resolving. If you suspect a reaction, stop using gel products and speak to your GP.
What is the difference between HEMA and Di-HEMA TMDDM?
Both are acrylate monomers used in gel polish. HEMA is a smaller molecule that penetrates skin more readily, making it a higher sensitisation risk. Di-HEMA TMDDM is larger, thought to penetrate skin less readily, and is the most common ingredient in HEMA-free formulas. It is lower risk, but not risk-free — it is still an acrylate.
Why was TPO banned in gel nail products?
TPO was identified as a skin sensitiser and banned in leave-on cosmetics under the EU Cosmetics Regulation. Gel nail polish counts as a leave-on product because it is cured onto the nail rather than rinsed off. UK guidance has followed a similar position. Brands reformulated to remove TPO, which is why ‘TPO-free’ began appearing on product pages from 2024 onwards.
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