Sun protection and hydration of stratum corneum: a study by 2-D differential method

The stratum corneum is the outermost layer of the skin. Its components and its morphology (such as the size of its cells) play a role in sun protection, and it has been noted that the stratum corneum hydration can change these properties. Sunscreens, applied on the skin, can be more or less effective depending on the stratum corneum characteristics. We therefore propose to simulate the quality of the sun protection and the effect of the stratum corneum hydration on the sun protection.

We first determined the sunscreen distribution on a plastic substrate using an optical coherence tomography device. We were then able to calculate, by 2-D differential method, the extinction of several sunscreens. We modelled the hydration of the stratum corneum, by changing the substrate with corneocytes of different thicknesses.

Our results showed that hydrated stratum corneum protects more against the UV. The benefit from changing the substrate varies depending on the sunscreen applied.

We modelled sunscreens on different substrates using electromagnetic simulations. To compare these results with measurements, we have to carefully hydrate or dehydrate the SC: the simulations did not take into account modifications of the surface (water on the surface for example) or any change in the characteristics of the stratum corneum other than the modification of the corneocytes thickness.