The importance of skin hydration after sun exposure.

Dry, normal, oily, combination or sensitive, regardless of its type, the skin needs water to maintain its suppleness and elasticity. Hydration is essential to prevent premature skin aging. However, in the face of certain external aggressions such as the UV rays of the sun, the skin dehydrates quickly. In response to this, after sun exposure, it is important to pay special attention to skin hydration for two main reasons:

• Compensate for the insensible water loss (IWL) that intensifies during exposure to the sun's UV rays.

  As a reminder, TEWL (Transepidermal Water Loss) is a phenomenon related to the passive diffusion of water and perspiration, leading to the constant and imperceptible evaporation of water from the dermis to the skin surface. This insensible diffusion through the various layers of the skin is essential for its normal functioning, as this physiological process promotes hydration of its superficial layers and also allows the rise of nutritive substances from the dermis to the epidermis, given that the latter is not vascularized. Under normal functioning, this loss amounts to 300 - 400 mL per day, but this value increases during sun exposure. To compensate for this water loss, it is therefore necessary to redouble efforts on hydration before, during, and after exposure.

• Maintaining your tan for a longer period.

  Hydration is a crucial step to extend your tan and delay peeling. However, it's important to note that a tan generally cannot last longer than a month due to cell differentiation. This natural process is characterized by the maturation of epithelial cells, which load up on keratin to become dead cells that make up the horny layer and eventually peel off. Thus, keratinocytes continually renew themselves in a cycle of approximately28 days.