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.

One of the key challenges facing TiO2 industry suppliers is the fluctuation of raw material prices. The production of TiO2 requires raw materials such as ilmenite or rutile, which are subject to market price volatility. Suppliers must carefully monitor these fluctuations and adjust their production processes accordingly to ensure profitability.

When manufacturers add titanium dioxide to foods and other ingestible products, it’s typically referred to as E171, which relates to food-grade purity.