Nail polishes are products that continue to grow in popularity, whether they're used for a special occasion or simply to add a bit of color to everyday life. Their use dates back thousands of years, with archaeological digs uncovering nail polishes that were used 6,000 years before our era. Back then, the formulation of nail polishes was different and primarily based on henna. The darker the color, the higher the social status of the person wearing it. Today, nail polishes come in an endless array of versions (classic polishes, semi-permanent polishes, permanent polishes, peel-off polishes...) and colors (shiny, matte, pastel, metallic, glittery...). However, they all operate on a similar principle: applying a waterproof layer to the nails.
Even though it might be tempting, one should not keep nail polish on for too long.
Indeed, beneath its rigid exterior, the nail is a delicate structure. It is primarily composed of keratin, a fibrous protein also found in skin and hair, organized into compact layers. To maintain flexibility and strength, this structure needs to be hydrated, but not excessively. However, when a nail is covered for too long, its hydration level increases, making it soft and fragile. This is due to the structure of the nail's keratin. Being permeable and porous, it can absorb up to 40% of its weight in water. However, when keratin swells, the layers that make up the nail separate, and the nail can split.
Furthermore, to ensure the structure and durability of nail polishes, solvents, polymers, plasticizers, and resins are incorporated into their formulation. However, prolonged exposure to these molecules can weaken the natural lipids of the nails, thereby altering their structure. In addition, the pigments found in nail polishes can cause residual discoloration on the nail surface, often yellow-orange, due to their infiltration. Keeping a polish on for a long time also promotes the accumulation of micro-cracks in the nails, especially in the case of rigid polishes, like the semi-permanent polishes or the permanent polishes. These cracks can become entry points for pathogens, which can potentially cause a fungal infection or a paronychia, for example.