Facts: Titanium dioxide and zinc oxide are minerals frequently used as physical solar filters in sunscreens. These chemicals scatter ultraviolet radiation away from the skin, compared to the chemical sunscreens that absorb various wavelengths of ultraviolet radiation. To this day, there is no evidence stating that these solar filters used in common sunscreens pose any health threat to human skin, including the formation of skin cancer. Even the risk from using nano-sized mineral sunscreens is considered negligible. To err on the safe side, avoid inhaling aerosol sprays with nano-sized particles (of any substance)!
While titanium dioxide and zinc oxide have not been shown to cause cancer, the sun has. The World Health Organization considers ultraviolet tanning beds carcinogenic to humans. Today, the Food and Drug Administration (FDA) explicitly allows marketing of broad-spectrum sunscreens with a SPF greater than 15 to claim that appropriate use can lead to reduction in skin cancer risk.