Nano is Bigger! Issues and Challenges with Nanoparticulate UV-Filters (NP-UVF).

Preparations containing pigments have been used since ancient times to protect against negative effects of solar radiation. In the 1950s, first sunscreens containing particulate ZnO and TiO2 appeared. Particle sizes in these products were such that light was scattered and reflected rendering preparations highly visible on skin. They were soon considered cosmetically unattractive. By reducing size of the particles to the range of less than 100 nm, sunscreen products appear transparent on skin because the particles no longer primarily reflect radiation but absorb it, predominantly over a large range of the UVB-UVA spectrum.