How long does it take to tan?

When you expose your skin to the sun, it tans and darkens. This is a protective mechanism to resist UV rays, which can accelerate skin sagging and causehyperpigmentation, sunburn or skin cancers.

Tanning is the result of the melanogenesis process, that is, the synthesis of melanin, a brown pigment, in the skin. UV rays penetrate the epidermis and reach the melanocytes, globular cells located in the basal layer of the epidermis containing organelles called melanosomes. Melanocytes are in contact with keratinocytes, which are present in every stratum of the horny layer. The synthesis of melanin involves a series of reactions, the final step of which is the conversion of tyrosine, an amino acid, by the enzyme tyrosinase.

The melanosomes are then transferred from the melanocytes to the keratinocytes to enable pigmentation and, most importantly, the protection of the epidermis by melanin. Following this, the melanosomes are destroyed. Melanin functions by enveloping the nucleus of the keratinocytes to form a filter that protects the DNA from the mutagenic and carcinogenic effects of UV rays. This pigment is capable ofabsorbing approximately 50% of UVA and 85% of UVBthat manage to reach the skin. Melanin can also capture free radicals generated within the body by UV radiation, thus limiting the premature ageing of the skin.

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

The time required to tan varies from person to person and also depends on environmental conditions. To avoid redness and skin dryness, here are the various factors to consider when calculating your tanning time.

• Their phototype.

  The very first factor to consider before sun exposure is one's phototype. This concept encompasses an individual's skin tone and the ability of their skin to tan without burning. The most commonly used classification today is that of Fitzpatrick, distinguishing 6 phototypes, from the lightest to the darkest. Individuals with phototype I and II particularly struggle to tan and frequently experience sunburn. Therefore, they should expose themselves to the sun for shorter periods than those with darker skin, to avoid reddening instead of browning.

• The degree of sun exposure.

  It may seem obvious, but the time required to tan will not be the same if the sun is shining high in the sky or if the weather is overcast. It remains possible to tan if clouds are present but, as these block on average 30 to 60% of the sun's rays, this will require a longer exposure time.

• The position of the sun.

  It is when the sun is high in the sky that its rays are most intense. Indeed, the distance travelled by UV rays through the atmosphere to reach the Earth's surface is less in this case. As a result, they are less dispersed and encounter fewer air molecules that can absorb or scatter the UV rays.

• The location where you expose yourself.

  The location of exposure also has an impact on the tanning time. Indeed, you will tan faster if you are surrounded by snow, sand or if you are floating on water, as these different elements reflect the sun's rays. This is why it is very important to apply sunscreen during winter holidays in the mountains, due to the strong reflection of light by the snow.

• Ambient humidity.

  Surprisingly, the humidity level of the place where you tan can impact the time it takes for the skin to pigment. In fact, when in a humid place, the epidermis is less prone to dehydration caused by sun exposure. As a result, it develops fewer redness and tans more quickly.