Sulphate process. The ilmenite is reacted with sulphuric acid giving titanium sulphate and ferric oxide. After separation of ferric oxide, addition of alkali allows precipitation of hydrous titanium dioxide. The washed precipitate is calcined in a rotary kiln to render titanium dioxide. The nucleation and calcination conditions determine the crystalline structure of titanium dioxide (e.g. rutile or anatase).

Most food-grade titanium dioxide is around 200–300 nanometers (nm) in diameter. This size allows for ideal light scattering, resulting in the best color (1Trusted Source).

Assessment of biocompatibility in prokaryotic cells

In short, no, research demonstrates that E171 is safe when consumed in normal situations.

Moreover, how we're exposed to an ingredient matters significantly in terms of our health and potential toxicity.   

Research shows that inhaling titanium dioxide particles in significant quantities over time can cause adverse health outcomes. Unless you work in an industrial setting, inhaling substantial amounts of titanium dioxide is highly unlikely. 

Research supports that applying titanium dioxide to the skin in the form of sunscreens, makeup, and other topical products does not pose a health risk. 

Overwhelmingly, research that's relevant to human exposure shows us that E171 is safe when ingested normally through foods and drugs (1,2).

Again, other research suggests that E171 could cause harm; however, those research processes did not design their studies to model how people are exposed to E171. Research that adds E171 to drinking water, utilizes direct injections, or gives research animals E171 through a feeding apparatus is not replicating typical human exposure, which occurs through food and medicine consumption.

Read more in-depth about the titanium dioxide risk at go.msu.edu/8Dp5.