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.

4.3 g/Cm3

Lithopone is produced by coprecipitation of barium sulfate and zinc sulfide. Most commonly coprecipitation is effected by combining equimolar amounts of zinc sulfate and barium sulfide:

There are two primary forms of titanium dioxide commercially available: anatase and rutile. The rutile form is typically used in sunscreens due to its superior ability to handle UV rays and stability in the presence of UV light. The anatase form is typically used in other types of products, such as paint. Another plus of the rutile form is that its UVA protection extends past 400 nanometers, which is the upper limit of UVA.