How long can one keep nail polish on their nails?

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.

The recommended durations for keeping a polish on the nails vary depending on its type.

• Classic nail polishes: Classic nail polishes typically last for 3 to 7 days. Beyond this period, the polish often starts to chip and lose its shine.

• Semi-permanent nail polish: Semi-permanent nail polishes can easily last 2 to 3 weeks. It is recommended to remove them after this period to prevent prolonged occlusion of the nails.

• Permanent nail polish: Thicker and highly adhesive, permanent nail polish can last up to 4 weeks. Again, it is advisable not to exceed a one-month application, to avoid weakening the nails.

Furthermore, it is advised to observe rest periods between different nail polish applications. This allows the nails to regenerate, rebuild their lipid barrier, and rebalance their water content by being in contact with the environment again. Between two applications of regular nail polish, it is beneficial to wait a few days. Regarding semi-permanent or permanent nail polishes, we recommend observing a break of 2 to 3 weeks. During this period, don't hesitate to hydrate and nourish your nails with plant oils, nail serums, or even strengthening nail polishes, in order to restore their structure.