By Stellar Gel The Intersection of Cosmetic Chemistry and Professional Nail Technology
If you follow international cosmetic news, you might have heard the rumblings: TPO is on its way out.
For decades, TPO (Trimethylbenzoyl Diphenylphosphine Oxide) has been the superstar ingredient in clear builder gels, white gels, and top coats. It’s the reason your clear builder doesn't turn yellow and why your pigmented whites cure all the way through.
But recent regulatory changes in Europe have classified TPO as a Reprotoxic 1B substance (meaning it may damage fertility or the unborn child). As a result, major brands are scrambling to reformulate. The most common replacement? A chemical cousin called TPO-L.
But this begs the question: If they sound almost the same, is TPO-L actually safer? Or is it just a legal loophole?
At Stellar Gel, we believe in radical transparency. We are currently in the process of removing TPO from our entire global supply chain (a goal we are on track to hit by 2026), and our Made in USA line is already completely TPO-Free.
Today, we are putting TPO and TPO-L under the microscope to explain the difference, the safety data, and the future of your favorite gels.
What is TPO and Why Do We Use It?
To cure gel, you need a Photoinitiator. This is the molecule that absorbs UV/LED light and kicks off the hardening process.
Different photoinitiators absorb different wavelengths of light.
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TPO is unique because it absorbs light in the "long wave" UVA range (380nm–420nm).
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Why that matters: Long waves penetrate deeper. TPO is critical for curing thicker layers (like builder gel) and highly pigmented colours (like black, white and darks) where light struggles to reach the bottom.
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The Yellowing Factor: Unlike older photoinitiators, TPO doesn't yellow over time. This makes it essential for crystal-clear builder gels.
For years, it was the gold standard. Until the safety data caught up.
The Ban: Why TPO is Being Removed
The European Union’s scientific committee (SCCS) reviewed TPO and reclassified it as Reprotoxic Category 1B.
What does this mean?
It means that in high concentrations (orally in animal studies), there is evidence that it can adversely affect reproductive health. While the risk to a client getting a manicure once a month is statistically very low (especially since the gel is cured into a solid), the risk to the nail technician handling liquid gel daily is higher.
Because of this classification, the EU is banning TPO in cosmetic products. Since the EU sets the global trend for safety, responsible brands like Stellar Gel are removing it worldwide, not just in Europe.
Enter TPO-L: The Liquid Alternative
As TPO exits the stage, TPO-L (Ethyl (2,4,6-trimethylbenzoyl) phenylphosphinate) is entering the spotlight.
Chemically, they are very similar. They belong to the same family of phosphine oxides. They both absorb long-wave UV light. They both cure deep and clear.
The Physical Difference:
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TPO is a yellow powder (Solid).
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TPO-L is a yellow liquid.
Because TPO-L is a liquid, it blends into gel formulas much easier. You don't have to worry about dissolving powder grains (which can sometimes leave un-dissolved specks in your gel).
The Big Question: Is TPO-L Actually Safer?
Short Answer: Yes, according to current science.
Here is why TPO-L is considered a safer alternative to TPO, and why it is allowed in our "safer" formulations:
1. Lower Reactivity & Volatility
TPO-L is a larger, heavier molecule in its liquid state. It has lower volatility, meaning fewer molecules escape into the air you breathe.
2. The Regulatory Status
Currently, TPO-L is NOT classified as a Reprotoxic 1B substance.
Extensive testing has shown that it does not carry the same high-level reproductive risks as solid TPO. It is fully approved for use in the EU, USA, and Asia.
3. Solubility
Because TPO-L is a liquid that is fully miscible (mixable) with the gel resin, it integrates better. This leads to a more uniform cure. A uniform cure means fewer "free monomers" leaching out of the gel after it hardens, which reduces the overall allergy risk for the client.
Is It Perfect? (The "Regrettable Substitution" Risk)
We want to be honest: TPO-L is safer, but it is not water. It is still a chemical photoinitiator.
In the world of chemistry, there is a concept called "Regrettable Substitution" ~ replacing a toxic chemical with a similar one that turns out to be just as bad 10 years later (like replacing BPA with BPS in water bottles).
While TPO-L is currently cleared and deemed safe, Stellar Gel’s chemists are constantly monitoring the data. We use TPO-L because it is the safest effective option currently available to cure pigmented gels without TPO.
However, for clients who are ultra-wary of any phosphine oxides, we offer the ultimate solution: The Made in USA Line.
The Stellar Standard: How We Are Protecting You
We are taking a two-tiered approach to this industry shift.
1. The Global Transition (China Line)
We are actively reformulating our entire massive library of 300+ colors and builders produced in China. We are replacing TPO with TPO-L and other advanced photoinitiator blends. Our goal is to be 100% TPO-Free across the board by early 2026, putting us ahead of many competitors who are waiting until the last minute.
2. The Gold Standard (USA Line)
For our Made in USA products, we don't need to wait. They are already there.
Our USA-manufactured gels are formulated 3-Free under our strict definition:
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No HEMA
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No HPMA
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No TPO
If you have a client who is pregnant, breastfeeding, or simply concerned about reproductive toxins, our Made in USA collection is the safest choice you can offer them.
Conclusion: Future-Proofing Your Salon
The "TPO Ban" sounds scary, but it’s actually a sign of progress. It means the industry is paying attention to health.
You don't need to throw away your current collection overnight, but you should start reading labels. By switching to Stellar Gel, you are partnering with a brand that is proactively cleaning up its chemistry before the laws even require it.
Safe. Cured. Compliant.
That’s the Stellar promise.
Disclaimer: This article is for educational purposes regarding cosmetic regulations. While TPO-L is currently considered safe by regulatory bodies, always use proper ventilation and PPE when working with uncured gel products.