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Consumer Products

What’s that Stuff

What is gel nail polish, and how does it create durable manicures?

Light-triggered chemistry opens up a range of nail options

by Brianna Barbu
June 4, 2023 | A version of this story appeared in Volume 101, Issue 18


A hand under a curing lamp for gel nails.
Credit: Shutterstock

Peruse the service menu at any nail salon, and you’ll be confronted with a staggering array of choices for your manicure: exfoliation, extensions, a rainbow of colors, tips, intricate nail art, and more.

If you’re looking for a simple pop of color and a glossy finish, the first decision you’re likely to make is what kind of nail polish to get: regular or gel. Bottles of both types of polish are often lined up next to each other, with different-colored caps denoting at a glance which is which.

Structure of 2-hydroxyethyl methacrylate.

The first difference you might notice between gel and regular polish is the price: gel polish is more expensive. But, your nail tech might tell you, it hardens in less than a minute with the help of a special curing lamp, and it’s much less likely to chip. The downside is that gel is more difficult to remove: it has to be soaked—or in some cases filed—off, rather than coming off with a quick wipe.

All those different properties are due to regular and gel polish having very different chemistries.

Nailing the science

“Whatever we put on our nails has to behave like an industrial coating, and yet at the same time be aesthetically pleasing and come off easily,” says Frank Pagano, a cosmetic chemist who worked on nail polish formulation at Revlon for a decade. With a $2.3 billion market in the US, according to the market research firm Mintel, the nail care industry offers a multitude of products that reflect the range of things consumers might prioritize. Want something quick drying and chip resistant? Gel might be your friend. Want to be able to easily change your look at home? Maybe stick with regular.

Structure of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

All nail polishes are polymeric coatings applied on top of natural nails. The variation comes from which type of polymers they are. Regular nail polish is based mostly on nitrocellulose and hardens after solvent evaporation. Gel, acrylic, and powder, or “dip,” nails are all based on acrylic polymers, and the polymerization is part of the application process. Gel refers specifically to nail coatings in which the polymerization is triggered by light.

Many drugstore companies offer polishes that have “gel” in the name but are often just regular nitrocellulose-based polishes with fancy copolymers added to make them more chip resistant. If you don’t have to stick your hand under a lamp to harden your manicure, it’s not a gel.

When it comes to the details of the chemistry, “gel nail polish is like a play,” Pagano says. “You’re gonna have certain characters; it’s just a question of who’s playing the characters.” The stars of the show are the monomers and the photoinitiator, which cues those monomers to link up into polymer chains.

The photoinitiator’s role is to absorb ultraviolet light and split into radicals that kick-start polymerization. Two commonly used photoinitiators are benzoyl peroxide and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

The monomers that the photoinitiator pushes to polymerize are a mixture of various methacrylates. Hydroxyethyl methacrylate (HEMA) is a major component of many gel polishes; di-HEMA trimethyl- hexyl dicarbamate, another common ingredient, has two methacrylate groups so it can function as a cross-linker between polymer chains. There may also be a couple of other small methacrylates in the formula, as well as oligomers or polymers with reactive methacrylate groups. The interconnected polymer network these compounds form gives gels their chip resistance and staying power.

By tweaking the combination of building blocks, the same light-triggered reaction can be used to create polymer coatings with a range of properties. According to Emily Nagy, a licensed nail technician in Michigan, there are two main categories: soft gels, which have a flexible polymer network and can be removed by soaking them in solvents such as acetone; and hard gels, which are rigid and impermeable to solvents and must be filed off. Gels can also vary in viscosity, from the thin polish used for color coats to thick builder gels and even thicker moldable gels used for creating 3D nail designs.

A bottle of gel polish also contains plenty of supporting actors: stabilizers, rheology modifiers, preservatives, solvents, and, of course, pigments. Formulation scientists work hard to create a base formula that functions correctly and consistently for the whole product line and makes it easy to swap out the pigments. Cosmetic chemist Kelly Dobos says that “the consumer should expect the same thing every time,” no matter what molecule or mineral provides the color.

Illuminating safety

Nagy says her training to become a certified nail tech was largely focused on hygiene and how to prevent nail infections, which is important for all manicures. So is ensuring adequate ventilation to minimize the amount of volatile organic solvents hanging around in the air. But gels raise a couple of safety questions that traditional polishes don’t.

One concern is whether the ultraviolet from the lamps damages skin, as there are well-established links between UV and skin aging and cancer. Newer LED curing lamps, which deliver a narrower wavelength of light than fluorescent UV lamps, are supposed to be make the curing process faster and safer. But UV light is still essential to any gel manicure.

Structure of the 2,2,4 isomer of di-HEMA trimethylhexyl dicarbamate.

A study published earlier this year in Nature Communications (DOI: 10.1038/s41467-023-35876-8) found that an LED nail dryer caused DNA damage to mouse and human cells in vitro. But other studies suggest that it would probably take a lot of time under the lamp to reach a threshold for serious damage to your hands (JAMA Dermatol. 2014, DOI: 10.1001/jamadermatol.2013.8740). Still, because UV damage is cumulative over a lifetime, the American Academy of Dermatology recommends that people who regularly get gel manicures protect their skin with sunscreen.

Some ingredients in the polish also come with safety concerns. Methacrylates are skin irritants and sensitizers—people can become seriously allergic to them over time. And if that happens, there are bigger consequences than having to switch to regular nail polish: acrylates are used in a number of medical products, such as bone cement, dental fillings, and diabetic insulin pumps, that a person with such an allergy would not be able to tolerate.

In a study performed by the British Association of Dermatologists, 2.4% of people tested at dermatology clinics showed an allergic reaction to at least one methacrylate compound.

Cosmetic Ingredient Review, a US personal care product safety nonprofit, has concluded that acrylates in nail products are safe to use as directed. Nails aren’t very porous, so the short amount of time that the uncured monomer is on them is unlikely to cause harm. If there’s minimal contact between uncured nail polish and the skin around your nails—which a good nail tech will ensure—gel manicures are considered safe. In the EU, regulations say products containing HEMA and di-HEMA trimethylhexyl carbamate are for professional use only.

But DIY manicures have had an uptick in popularity since the pandemic. According to a 2021 survey by Mintel, 25% of 1,412 respondents said they had used gel nail polish at home.

Most drugstore brands that sell at-home gel kits in the US make ingredient and safety information available on the packaging and on their websites, as required by the US Food and Drug Administration, but some sites make it easier than others to find that information.

For your health and that of your nails, “it’s really important to think about . . . going to a professional” if you want a gel manicure, Dobos says.

Nagy recommends that clients find a nail tech who educates themselves on the evolving landscape of nail products and keeps an open dialogue with clients about any health or safety concerns they might have. “The burden of information needs to be on the nail technician and not on the client.”


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