While nano-sunscreens are considered very effective, a new Aussie modelling study has claimed that even the most effective nanoparticles in some invisible sunscreens might be the most toxic.
Dr Amanda Barnard of CSIRO Materials Science and Engineering in Melbourne carried out her computer simulation of titanium dioxide nanoparticles.
Nanoparticles are used to make some sunscreens transparent, increasing their appeal to some consumers.
"There's a whole range of demographics that would never ever use sunscreens if they were ugly," ABC Science quoted Barnard as saying.
"The transparent ones do increase usage and protection from skin cancer in certain demographics, so they do have an important function," he added.
However, she said that many doubts have been raised about the safety of such sunscreens.
One particular concern is whether the nanoparticles interact with sunlight to produce free radicals that damage tissues or DNA.
Barnard's computer model examined titanium dioxide nanoparticles from 3 to 200 nanometres in size.
"This is the size range that would generally be used in different types of sunscreens," she said.
The model predicted the affect of nanoparticle size and concentration on sun-protection ability, transparency and potential to produce free radicals.
It was found that the size and concentrations of nanoparticles that gave the best transparency and sun protection also gave the highest potential for production of free radicals.
"Where we have the highest sun-protection factor - and it's pretty - it [the sunscreen] is also toxic, potentially," said Barnard.
She found that only particles less than 13 nanometres in size would minimise free radical production while maximising transparency and sun protection.
The study has been published in the latest issue of Nature Nanotechnology. (ANI)