Both P25TiO₂NPs (with or without vitamin B2) were not found beyond the epidermis in 99% of the analyzed TEM images (Fig. 8). This is coherent with previous findings showing that nanoparticles greater than 50 nm can not penetrate the skin, even in vivo models with movement, stretching, and friction [54]. However, in one of the zones, a few nanoparticles were observed inside a hair follicle. This could be due to the follicle exposure after the localized rupture of this physical barrier when rats were shaved in order to clean the area for cream topical administration. This finding suggests that nanoparticle-based sunscreen should not be applied on recently shaved or harmed skin, in order to avoid nanoparticle skin penetration.

To put this all into context maybe we should go back to the beginning & Bluescope steel who make all of our lovely Australian colour bond iron roofs.

Lithopone, white powder, relative density: 4.136 ~ 4.39 g / mL, insoluble in water. It is a mixture of zinc sulfide and barium sulfate. Inorganic white pigment, widely used in plastics such as polyolefin, vinyl resin, ABS resin, polystyrene, polycarbonate, nylon and polyoxymethylene, and white pigments of paints and inks. It is less effective in polyurethane and amino resins and less suitable in fluoroplastics. It is also used for coloring of rubber products, paper, varnish, tarpaulin, leather, watercolor paint, paper, enamel, and the like. Used as a binder in the production of electric beads.

While the anatase titanium dioxide market is robust, it faces challenges such as regulatory compliance and environmental concerns related to extraction and processing. Manufacturers are increasingly adopting sustainable practices, focusing on recycling materials and minimizing waste in production processes. Innovations in nanotechnology are also leading to the development of more efficient and eco-friendly synthesis methods that can further enhance the properties of anatase TiO2.