They are the only two sunscreen ingredients classified by the FDA as safe and effective. And though titanium dioxide is usually used in mineral sunscreens in the form of nanoparticles, evidence suggests that few, if any, particles penetrate the skin.

Fig. 7. Lipid peroxidation measured on samples of MSSA with: A) 0.2 mg/mL P25TiO₂NPs; B) 0.02 mg/mL P25TiO₂NPs; C) 0.2 mg/mL VitaminB2@P25TiO₂NPs; D) VitaminB2@P25TiO₂NPs 0.02 mg/mL after 3 h of irradiation (red) and 6 h (blue). MDA could not be detected after 6 h of irradiation in a sample with P25TiO₂NPs. Error bars are too small to be seen in graphic and p < 0.05 between C-D and A-B.