Suncreen nanoparticles 'might be toxic'
Nanoparticles used to make some sunscreens transparent, making them popular with consumers, might also be toxic according to Australian research which adds to uncertainty about the safety of some sunscreens.
A study by Amanda Barnard, from the CSIRO's materials science and engineering division, found the nanoparticles that provided the best transparency and sun protection also represented the highest for production of free radicals.
Using computer modelling, Dr Barnard analysed the properties of the man-made titanium dioxide nanoparticles found in some sunscreens, testing them in three areas: sun protection, transparency and potential for free radical production.
Studying various sizes of particles, she found it was a case of the smaller the nanoparticle the better the sun protection and transparency.
"Unfortunately the small ones also have a high surface-to-volume ratio and the surfaces are where the free radicals are produced through a photochemical, or light induced reaction," she said.
Dr Barnard won the 2009 Malcolm McIntosh Prize for physical scientist of the year for her work on nanoparticles — tiny particles used in many products including sunscreens, cosmetics and paints.
Her latest research, published next month in the journal Nature Nanotechnology, found only particles less than 13 nanometres in size minimised free radical production while retaining other desirable properties.
The titanium dioxide nanoparticles in sunscreens range in size from three to 200 nanometres.
The results add to questions about the safety of such sunscreens. The main concern is whether the nanoparticles interact with sunlight to produce free radicals that damage tissues or DNA. "There's a trade-off to be made here," she said. "Currently it's a situation of 'is it better to protect yourself from UV rays or hold off and see what happens'. But in the future it may be 'is it better to protect yourself from UV rays or protect ourself from something else'," she said.
However Dr Barnard stressed that it was still unclear if nanoparticles found in sunscreen penetrated the skin — and if they did, what happened once they entered the corrosive environment of the human body.
"We don't want to discourage people from doing something that could save them from skin cancer on the off chance that something may be found in sunscreens," she said.
A spokeswoman for the Therapeutic Goods Administration said the study raised some interesting ideas, however "the findings are predicated on a number of assumptions that do not necessarily reflect real life situations or actual product formulations".
According to the TGA's website, current evidence suggests titanium dioxide nanoparticles in sunscreens are not a risk because they remain on the surface of the skin.
Similarly, the Cancer Council Australia website states nanoparticles used in sunscreens do not pose a risk. "However ... welcome any new research that sheds more light on this topic."