What is the best time to tan?

Tanning refers to the skin pigmentation that occurs as a result of sun exposure. From a biological perspective, UV rays stimulate the synthesis of melanin by melanocytes, which are cells in the epidermis. This is a defense mechanism designed to limit the harmful effects of UV rays on the skin, which can accelerate skin sagging and cause hyperpigmentation, sunburn , or skin cancers.

Melanin functions by enveloping the nucleus of keratinocytes, the cells of the stratum corneum, where it forms a filter that protects DNA from the mutagenic and carcinogenic effects of UV rays. This pigment is capable ofabsorbing approximately 50% of UVA and 85% of UVB rays that reach the skin. Melanin can also capture free radicals generated within the body by UV radiation, thus limiting the premature aging of the skin.

Important : While the process of melanogenesis occurs to protect the skin from UV rays, it does not exempt the need to use a broad-spectrum sunscreen on areas of the body exposed to the sun, and to reapply every two hours.

Indeed, sunbathing requires sunlight, but it should not be too intense. Specifically, between 11 a.m. and 4 p.m., when solar radiation is at its peak, the skin is more likely to burn and suffer from sunburn than to tan.

Thus, to limit skin dryness while tanning, it is recommended to expose oneself to the sun in the morning, between 9:30 and 11:00, or in the late afternoon, between 4:00 and 7:00. It's also worth noting that it's not advisable to have more than one tanning session per day, as it is more effective and safer to tan gradually.

It is possible to tan in any season, even in winter. In fact, the presence of snow makes tanning more effective, as this element is capable of reflecting up to 85% of UV rays. However, between the ski suit, protective glasses, and hat, one might end up with a rather haphazard tan.

Tanning sessions are therefore typically when the weather is clear and sunny, usually between late spring and early fall. However, it is crucial to exercise extra caution during the summer, when the sun's rays are hotter and more intense, and to never forget your hat and sunscreen. If UV rays are more energetic in the summer, it's because of the Earth's tilt angle, which does not rotate vertically around the sun but is slightly tilted (≈ 23°). The sun's rays therefore strike either the North or South Pole depending on the time of year, which explains why the seasons are "reversed" at each pole.

Finally, if you notice some clouds in the sky, rest assured, this will not prevent you from tanning. Indeed, only large dark clouds are capable of blocking all UV rays. A mid-altitude cloud layer can only stop 30 to 60% of the sun's rays. Moreover, if the clouds are white and scattered, the UV rays will reflect and the radiation will then increase by 10%.

• ANANTHASWAMY H. Toxic effects of ultraviolet radiation on the skin. Toxicology and applied pharamcology (2004).

• SITUM M. & al. UV-radiation, apoptosis and skin. Collegium Antropologicum (2011).