What Is In Gel Nails

The gel nails are essentially a light-curing resin system, mainly composed of 3 chemical cores: oligomers (to provide strength and gloss), monomers (to provide flexibility and adhesion), and photoinitiators (to trigger the hardening reaction under UV/LED light).

From a health and safety point of view, modern formal nail polish products usually no longer contain volatile “three toxins” such as formaldehyde or toluene. But I have to remind those consumers who are concerned about ingredients that what you really need to be wary of is HEMA (hydroxyethyl methacrylate). This is the specific monomer used to increase adhesion. Although it works extremely well, according to industry data, HEMA is currently the leading cause of allergic contact dermatitis in the nail industry.

Therefore, as long as you choose a high-quality (preferably HEMA-free) formula and ensure that they are fully cured under the light, the nail polish will become a chemically inert plastic structure that is safe and will not release toxins into the body.

Three Chemical Pillars Of Nail Polish

To really understand what’s in the nail polish, we can’t just look at the color; we must go deep into the chemistry that makes the product unique. Unlike traditional nail polish, which is dried by evaporation, the gel hardens through a chemical reaction driven by these three main ingredients:

Oligomer-Skeleton:

These are short-chain molecules that give the gel that sticky, gelatinous texture before it solidifies. Oligomers play a big role in the formulation; they are responsible for building the physical structure of artificial nails, providing the durability, hardness, and high gloss that nail art is known for.

Monomer-Thinner And Glue:

Monomers are smaller single molecules that act as solvents to dissolve oligomers. They control the texture of the nail polish, giving it spreadability. More importantly, the monomer provides flexibility (to prevent the nail from cracking) and adhesion, and acts as a “glue” to bind the gel to the natural nail surface.

Photoinitiators-Trigger:

This is a class of light-sensitive compounds. When exposed to a specific wavelength of UV or LED light, the photoinitiator absorbs energy and splits, starting a chain reaction that links the oligomer and monomer together. This process transforms the liquid gel into a solid, durable coating.

What Is “Nothing” In Modern Nail Polish

When studying the composition of nail polish, it is equally important to understand what is eliminated from modern formulations. Historically, nail art products have been scrutinized for containing “three major toxins”: formaldehyde, toluene, and dibutyl phthalate (DBP).

Formaldehyde And Toluene:

These are volatile solvents commonly found in traditional air-drying nail polish.

Gel Difference:

This is a fundamental difference in formulation logic—because nail polish does not dry by evaporation but by curing, these volatile toxic solvents are usually not needed at all in gel formulations. The reputable brand of modern nail polish has eliminated these harmful substances in chemical engineering design and instead focused on the 100 percent reactive solids (oligomers and monomers) I mentioned above.

The HEMA Controversy: The Game Of Adhesion And Allergy

Although modern gels avoid the “big three toxins,” the composition list still needs to be carefully reviewed, especially with regard to HEMA (hydroxyethyl methacrylate).

HEMA is the specific monomer widely used in the industry because it is composed of very small molecules. In the lab, it is clear that these small molecules can easily penetrate the surface of natural nails to create superior adhesion and long-lasting nail effects.

However, the chemical nature of HEMA’s effectiveness—its small molecular weight—is also the risk. Because it can easily penetrate the skin barrier, HEMA is considered the number one allergen in nail art products. Repeated skin contact with uncured HEMA results in allergic contact dermatitis, a lifelong immune response.

This situation has led to the rise of “HEMA-free” formulations, which use higher molecular weight monomers to reduce the risk of skin penetration and allergies. Although there may be a slight compromise in adhesion, this is usually worth it.

The Importance Of Complete Curing

The final piece of the puzzle to understand “what’s in the polish gel” lies in the state of matter itself. The safety of the ingredients depends largely on the curing process.

Liquid Vs. Solid:

In the liquid state, the monomers and oligomers are reactive.

Chemically Inert Structure:

When a high-quality gel is applied correctly and cured for a sufficient amount of time under a suitable UV/LED lamp, a complete chemical reaction will occur. The components cross-link to form a hardened plastic polymer.

Once fully cured, the nail polish becomes chemically inert. This means that the structure is stable and does not leach chemicals or toxins into the body.

However, if the gel is not sufficiently cured (due to weak lamp power or too thick application), uncured monomers—including HEMA—will become trapped inside, posing a risk of allergic reactions.

So, the safety of the gel on your nails is ultimately determined by the quality of the formula and the accuracy of the operation.

Author: Sarah Jenkins

“I am Sarah Jenkins, a certified nail technician and cosmetic chemistry researcher. My work focuses on demystifying the science behind nail products, specifically analyzing the interaction between Oligomers, Monomers, and UV curing. I am dedicated to helping readers understand ingredients like HEMA to ensure their gel manicures are both beautiful and chemically safe.”