A significant body of research, mostly from rodent models and in vitro studies, has linked titanium dioxide with health risks related to the gut, including intestinal inflammation, alterations to the gut microbiota, and more. It is classified by the International Agency for Research on Cancer (IARC) in Group 2B, as possibly carcinogenic to humans.

The concern from animal studies is that high amounts of titanium dioxide have increased inflammation and colon tumor formation, said Dr. Johnson-Arbor. A 2021 review, meanwhile, suggested that using titanium dioxide as a food additive weakens the gut lining and worsens the progression of inflammatory bowel disease.