Another important application of titanium dioxide is in the production of sunscreen and other skincare products. Titanium dioxide is a key ingredient in many sunscreens due to its ability to reflect and scatter ultraviolet (UV) radiation, providing protection against harmful UV rays. Manufacturers of titanium dioxide for sunscreen products often use special coatings and surface treatments to enhance its UV-blocking properties.

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.

CSPI says it might reconsider its rating if specifications for food-grade titanium dioxide in the U.S. are updated to ensure nanoparticles are minimized, and new studies are conducted to assess its capacity to cause cancer or other health problems. 

The vitaminC@P25TiO₂NPs, on the other hand, were obtained through an optimized method based on Mallakpour et al. [27]. Initially, 0.02 g of P25TiO₂NPs were dispersed in 1 mL of ultrapure water and stirred in a Vortex. Next, 100 μL of HCl (0.01 M) were added (pH 2) to 100 uL of P25TiO₂NPs to avoid gel formation. Then, 100 μL of vitamin C dissolved in ultra-pure water (5.0 × 10⁻³ M) solution were added to the mixture and was ultrasonicated for 30 min. Finally, vitamin C was added in excess to gain a beige-orange color suspension, and the ultrasonication continued for another 30 min. The pellet obtained after centrifuging the suspension for 10 min at 4500 rpm was resuspended in ultrapure water, centrifuged again, and then lyophilized.

What are the forms of titanium dioxide?