A 2023 study published in the journal Particle and Fibre Toxicology set out to examine the impact of titanium dioxide nanoparticles in mice “on the course and prognosis of ulcerative colitis,” by creating an ulcerative colitis disease model. Researchers found that the titanium dioxide nanoparticles significantly increased the severity of colitis. They also “decreased the body weight, increased the disease activity index and colonic mucosa damage index scores, shortened the colonic length, increased the inflammatory infiltration in the colon.” Researchers concluded: “Oral intake of TiO2 nanoparticles could affect the course of acute colitis in exacerbating the development of ulcerative colitis, prolonging the ulcerative colitis course and inhibiting ulcerative colitis recovery.”

In 2021, the European Food Safety Authority concluded that titanium dioxide is no longer safe in foods due to the same concerns over nanoparticles. As a result, titanium dioxide is now banned as a food additive in the EU. Although studies have shown that the absorption of ingested titanium dioxide is low, evidence suggests that titanium dioxide nanoparticles can accumulate in the body over time. Health Canada deemed it safe in 2022 but noted concerns. Unlike their European counterparts, Canadian officials did not consider studies performed with titanium dioxide nanoparticles alone. 

Titanium dioxide comes in the form of a white powder and is sometimes used in cosmetics to adjust a color to a lighter shade. This is also why it can produce a white cast.

White crystalline powder. It is a mixture of zinc sulfide and barium sulfate. The more zinc sulfide it contains, the stronger the hiding power and the higher the quality. Density 4.136～4.34 g/cm3, insoluble in water. It easily decomposes when exposed to acid to produce hydrogen sulfide gas, but does not work when exposed to hydrogen sulfide and alkaline solutions. It turns into light gray after being exposed to ultraviolet rays in the sun for 6 to 7 hours, but it still returns to its original color when placed in a dark place. It is easy to oxidize in the air and will agglomerate and deteriorate when exposed to moisture.