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.

In order to contribute with experimental evidence that could help to achieve a better understanding of the field for future regulation, in the present work, the biocompatibility of commercial P25TiO₂NPs (one type of TiO₂NPs used in sunscreen formulations) and two novel functionalized P25TiO₂NPs were evaluated under solar simulated irradiation. White light, generated by red, blue, and yellow LEDs, together with UV ones, was chosen to simulate the solar spectra. Functionalization of TiO₂NPs was made with antioxidant vitamins in order to prevent the expected photo-initiated ROS production when nanoparticles are exposed to the simulated solar spectra. Vitamin B2 (riboflavin) and vitamin C were chosen to carry out the functionalization because they are water-soluble, low-cost, and are a constitutive part of biological processes. In addition, it is known that both have the potential to prevent macromolecular oxidation by ROS [23], [24], [25], [26].