A review of the scientific literature on the safety of nanoparticulate titanium dioxide or zinc oxide in sunscreens

This paper reviews 24 different studies done on the use of titanium dioxide and zinc oxide in sunscreens and found that while there is some evidence from isolated cell experiments that these two nanoparticles can induce free radical formation in the presences of light that may damage these cells, this would only be a problem in the nanoparticles penetrated into viable skin cells. Overall, the majority of these studies seem to to suggest that these nanoparticles usually remain on the surface of the skin.