Evaluation of temporal scales of migration of cosmetic ingredients into the human skin by two-dimensional dynamic speckle analysis

A variety of biomedical and food quality assessment tasks have been solved by statistical processing of speckle patterns formed on the surface of diffusely reflecting objects. The output of pointwise processing of a temporal sequence of correlated speckle images is a two-dimensional spatial contour map which characterizes the time scales of the ongoing physical or biological activity within the studied objects. In this work, we check efficiency of the dynamic speckle analysis for temporal characterization of migration of cosmetic ingredients from the skin surface to the lower skin layers. At illumination with a He–Ne laser, formation of speckle patterns on the skin surface is governed by the diffusely reflected photons which have undergone a lot of scattering events in the bulk of the tissue. This entails low time-correlation of the formed speckle patterns. Activity maps have been built for sections of treated and non-treated skin on the arm of a volunteer. We found out that a bare skin exhibited high activity which decreased for a skin treated by a cream or cosmetic oil. We proved that the observed difference between the activity maps for a bare skin and a treated skin would allow for monitoring of the time scales of penetration of various cosmetic products into the skin to perform their quality assessment.