How long can one keep nail varnish on?

Nail varnishes are products that continue to grow in popularity, whether they are used for a special occasion or simply to add a touch of colour to everyday life. Their use dates back thousands of years, with archaeological excavations uncovering nail varnishes that were used 6,000 years before our era. At that time, the formulation of nail varnishes was different and primarily based on henna. The darker the colour, the higher the social status of the person wearing it. Today, nail varnishes come in an endless variety of versions (classic varnishes, semi-permanent varnishes, permanent varnishes, peel-off varnishes...) and colours (glossy, matte, pastel, metallic, glittery...). However, they all rely on a similar principle: applying a waterproof layer to the nails.

Even though it may be tempting, one should not keep nail varnish on for too long.

Indeed, despite its rigid appearance, the nail is a fragile structure. It is primarily composed of keratin, a fibrous protein also found in skin and hair, organised into compact layers. To remain flexible and strong, 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. Permeable and porous, it can absorb up to 40% of its weight in water. However, when the keratin swells, the layers that make up the nail separate and the nail can split.

Furthermore, to ensure the structure and durability of nail varnishes, solvents, polymers, plasticisers, 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 varnishes can cause residual discolouration on the nail surface, often yellow-orange, due to their infiltration. Keeping a varnish on for a long time also promotes the accumulation of micro-cracks in the nails, especially in the case of rigid varnishes, such as semi-permanent varnishes or permanent varnishes. These cracks can become entry points for pathogens, which may cause a fungal infection or a paronychia, for example.

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

• Classic nail varnish: Classic nail varnish is typically worn for 3 to 7 days. Beyond this period, the varnish often starts to chip and become dull.

• Semi-permanent varnishes: Semi-permanent varnishes 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 varnish: Thicker and highly adhesive, permanent nail varnish 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 varnish 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 varnish, it is beneficial to wait a few days. Regarding semi-permanent or permanent nail varnishes, we recommend observing a break of 2 to 3 weeks. During this period, do not hesitate to hydrate and nourish your nails with vegetable oils, nail serums, or even hardening nail varnishes, in order to restore their structure.