2. Cosmetics With its UV-filtering properties, anatase TiO2 is a popular ingredient in sunscreens and cosmetic formulations. Its ability to scatter UV radiation effectively protects the skin from harmful sun exposure, contributing to the increasing popularity of natural and mineral makeup products.

The vitaminC@P25TiO₂NPs, on the other side, did not have any effect on cell protection against ROS. This might be due to the fact that vitamin C, a well-known scavenger of ROS, could behave as prooxidant and even promote ROS and lipid peroxidation [39]. It was recently described that at small concentrations of vitamin C, the prooxidant effects dominate; while in large concentrations the antioxidant ones predominate [40]. The effect also depends on the cell state and the interaction of vitamin C with light. In this case, ascorbic acid may act as an antenna to harvest visible light when conjugated to P25TiO₂NPs. Indeed, it was previously found that this combination (in some ratios) could have an improved photocatalytic activity, possibly due to a red shift in its light absorbance [41]. Further studies on vitaminC@P25TiO₂NPs were not conducted, because of the poor antioxidant capacity [42].

In 2017, the Scientific Committee on Consumer Safety (SCCS) warned that they should revise their recommendations if any new evidence emerges in the future related to the potentially harmful effects of TiO₂NPs used in a sunscreen formulation or if they can penetrate the skin. In fact, our work could contribute to this matter because it evaluated the skin penetration of a particular kind of TiO₂NPs. [8]

Lithopone

≤0.3