Overexposure to sunlight can increase risk of skin cancer and sunscreens are often used for the protection against the skin-damaging ultraviolet rays.  However, consumers may not realize that sunscreen material titanium dioxide per se can induce DNA damage after it is exposed to sunlight.A report in FEBS Letters has found titanium dioxide a type of nanoparticles which is commonly used in sunscreens is not as safe as thought.  The report authored by John Knowland at University of Oxford in Oxford, UK and colleagues shows that the nanoparticles absorb about 70% of incident UV and in aqueous environments; they can lead to the formation of a type of free radical called hydroxy radicals which can initiate DNA damaging oxidations.The authors tested sunscreen titanium dioxide samples and found all catalyze the photo-oxidation of organic substrates and sunlight exposed titanium dioxide catalyzes DNA damage both in vitro and in vivo.