The main concern with nanoparticles is that they are so tiny that they are absorbed into the skin more than we want them (ideally sunscreen should remain on the surface of the skin). Once absorbed they might form unwanted complexes with proteins and they might promote the formation of evil free radicals. But do not panic, these are concerns under investigation. A 2009 review article about the safety of nanoparticles summarizes this, to date, in-vivo and in-vitro studies have not demonstrated percutaneous penetration of nanosized particles in titanium dioxide and zinc oxide sunscreens. The English translation is, so far it looks like sunscreens with nanoparticles do stay on the surface of the skin where they should be.  

4.3 g/Cm3

Despite these challenges, the TiO2 industry supplier continues to play a critical role in providing essential materials for a wide range of industries. With the growing demand for TiO2 in various applications, suppliers must continue to innovate and improve their processes to meet the needs of their customers.