What are the components of a nail polish?

For a special occasion or simply to add a bit of color to one's daily life, nail polishes are among the most popularly used products. There are various types (matte, glossy, semi-permanent, permanent...) to cater to everyone's needs and desires. The use of nail polish dates back further than one might think: archaeological excavations have unearthed nail polishes dating back to 6,000 years before our era. Of course, the formulations were very different back then. In ancient China and Egypt, henna leaves and clay were primarily used to dye nails in a brown-red color, a symbol of high social status. It is even said that Queen Nefertiti, wife of Pharaoh Akhenaton, often sported ruby red nails. Today, nail polishes are mainly composed of solvents (≈ 70%), film-forming polymers (≈ 15%), thermoplastic resins (≈ 7%), plasticizers (≈ 7%), pigments (≈ 1%) and suspension agents (≈ 1%).

Solvents: the liquid foundation of nail polish.

Nail polishes are primarily composed of solvents, which are necessary to ensure the blending of various ingredients and achieve a smooth, easy-to-apply texture. Solvents also facilitate the gradual evaporation of the product after application, leaving a solid and uniform layer on the nail. The main solvents used are ethyl acetate and butyl acetate, volatile solvents that evaporate quickly after the application of the nail polish, which is convenient for speeding up the drying process. Acetone, well-known for its role in nail-polish removers, is also sometimes used in small amounts in nail polishes to improve their fluidity. However, it is quite harsh on the skin and nails and tends to dry them out and weaken them. Solvents are essential to the formulation of nail polishes but are responsible for the strong odor of these products, which can sometimes bother sensitive individuals, such as pregnant women.

Polymers: The structure of nail polish.

Without polymers, nail polish wouldn't be able to form a solid film on the nail. These molecules are therefore essential for ensuring the adhesion, shine, and durability of the polish. The key ingredient in most nail polishes is nitrocellulose, a film-forming polymer that creates a thin, resilient layer. Nitrocellulose also imparts a natural glossy effect to the polishes in which it is incorporated. Historically, this polymer was the first medium used for film reels and was notably employed in the earliest reels of the Lumière brothers at the end of the 19th century. Acrylic copolymers are often added to nitrocellulose in nail polishes to enhance their flexibility and adhesion and prevent them from chipping too quickly. However, nitrocellulose is sensitive to heat, which explains why some polishes thicken over time.

Plasticizers: to prevent nail polish from cracking.

When it dries, a nail polish needs to be hard enough to withstand daily wear and tear (hand washing, use of household products, etc...) but not too rigid, so it doesn't crack with the slightest movement. This is where plasticizers come into play, molecules that make the texture of the polish more flexible and resilient. However, the majority of plasticizers are controversial. Notably, dibutyl phthalate (DBP), considered a potential endocrine disruptor, camphor, which is irritating in high concentrations, and triphenyl phosphate (TPhP), which also raises concerns about its impact on the endocrine system.

Resins: for enhanced nail polish adherence.

Often less known to the general public, resins are nonetheless important compounds for formulating a nail polish. They enhance the adherence of the polish to the nail and provide a glossy and uniform finish. The resins commonly found in nail polishes are formaldehyde resins, which are controversial due to their potential irritant and carcinogenic properties, acrylic resins, and alkyd resins.

Pigments and pearlescent substances: essential for nail polish color.

Nail polishes come in a multitude of colors and finishes due to the pigments and reflective particles they contain. The most popular are iron oxides and titanium dioxide, mineral pigments, used to achieve red or white shades, micas, providing a pearlescent or metallic effect, and organic dyes, used to achieve bright colors. It's worth noting that dark and highly pigmented nail polishes are often more difficult to completely remove from the nail surface.

Note : Some nail polishes also incorporate active ingredients to care for the nails, such as green tea, known for its softening properties, durian, recognized for its ability to strengthen keratin, or the avocado oil, which has a nourishing effect.