Distribution of ZnO nanoparticle containing formulations in skin measured by in vivo multiphoton fluorescence/SHG/HRS tomography

Objective: Among other scattering centers TiO2 and ZnO nanoparticles are commonly used as UV filters in commercial sunscreen products. Their penetration into the skin is controversially discussed in the literature. ZnO in biological tissue is harder to detect than TiO2 because zinc is also present in the human organism in dissolved form. Multi-photon tomography providing nonlinear effects can be used to investigate the penetration of ZnO nanoparticles into the human skin in vivo.