Finally, all of the studies reviewed on skin penetration were conducted without control for UV exposure. Therefore, no study has yet simulated the realife scenario for the application of sunscreens.
Future studies to determine the safety of ZnO and TiO2 nanosized particles in sunscreens should reproduce a human model for the realworld application of sunscreens including broken skin and accounting for UV exposure. These studies may, in addition, measure the potential penetration of ROS, formed on the stratum corneum from nanosized particles exposed to UV light into the upper layers of the epidermis.