In sunscreen, titanium dioxide is used as a barrier to keep the sun's ultraviolet (UV) rays from damaging your skin. It's processed into much smaller particles than what goes into food, called nanoparticles. In this form, it becomes transparent, and also absorbs UV light so it doesn't reach your skin.

In an early study Jani et al. administred rutile TiO₂ (500 nm) as a 0.1 ml of 2.5 % w/v suspension (12.5 mg/kg BW) to female Sprague Dawley rats, by oral gavage daily for 10 days and detected presence of particles in all the major gut associated lymphoid tissue as well as in distant organs such as the liver, spleen, lung and peritoneal tissue, but not in heart and kidney. The distribution and toxicity of nano- (25 nm, 80 nm) and submicron-sized (155 nm) TiO₂ particles were evaluated in mice administered a large, single, oral dosing (5 g/kg BW) by gavage. In the animals that were sacrificed two weeks later, ICP-MS analysis showed that the particles were retained mainly in liver, spleen, kidney, and lung tissues, indicating that they can be transported to other tissues and organs after uptake by the gastrointestinal tract. Interestingly, although an extremely high dose was administrated, no acute toxicity was observed. In groups exposed to 80 nm and 155 nm particles, histopathological changes were observed in the liver, kidney and in the brain. The biochemical serum parameters also indicated liver, kidney and cardiovascular damage and were higher in mice treated with nano-sized (25 or 80 nm) TiO₂ compared to submicron-sized (155 nm) TiO₂. However, the main weaknesses of this study are the use of extremely high single dose and insufficient characterisation of the particles.

Some websites maintain titanium dioxide is inferior to zinc oxide, another mineral sunscreen ingredient whose core characteristics are similar to those of titanium dioxide. The reality is that titanium dioxide is a great broad-spectrum SPF ingredient and is widely used in all manner of sun-protection products. What gets confusing for some consumers is trying to decipher research that ranks sunscreen ingredients by a UV spectrum graph. By most standards, broad-spectrum coverage for sunscreen ingredients is defined as one that surpasses 360 nanometers (abbreviated as “nm” - how the sun’s rays are measured). Titanium dioxide exceeds this range of protection, but depending on whose research you read, it either performs as well as or slightly below zinc oxide.

It is a white crystalline powder, which 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. The density of lithopone is 4.136~4.34/cm3 and it is 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.

In June 2022, Health Canada weighed in on the debate, releasing a report on the safety of titanium dioxide. Their expert panel reviewed toxicity studies, including ones involving genetic damage. The expert panel found that previous studies used different forms and properties of titanium dioxide and deliberately broke the material into smaller particles than what you would normally see in food.