Rub it in: Chris Nesnas lathers on the sunscreen at St Kilda beach on Monday. Photo: Joe Armao
Fears about dangers of nanoparticles in sunscreen may be unfounded, with research showing they are unlikely to harm beachgoers.
Scientists have for the first time been able to see how the body's immune system deals with zinc oxide nanoparticles - an ingredient found in many popular sunscreens.
Researchers from the Australian Synchrotron, the Melbourne Centre for Nanofabrication, CSIRO, RMIT and Monash University found while the body absorbed the nanoparticles, it could identify and remove them before they reached the bloodstream.
''This is the first time that we have shown that the cells of the immune system can break down the nanoparticles directly,'' said Australian Synchrotron and CSIRO bioinorganic chemist Simon James. ''Previous work was only able to infer that.''
Zinc oxide is added to sunscreen to absorb or scatter the sun's ultraviolet radiation and prevent sunburn. Unlike larger zinc particles that leave a white smear, nanoparticles are invisible to the eye, making products containing nanoparticles more popular with consumers.
Nanoparticles are also partially insoluble in water. But it had not been clear how the body dealt with those that penetrate the skin.
Researchers studied a type of white blood cell called a macrophage that was exposed to zinc oxide nanoparticles. They then counted how many tiny cube-shaped particles were absorbed.
Macrophages are key to the immune system and are the body's front-line rubbish disposal unit, removing foreign objects.
Dr James said on average 60,000 tiny nanoparticles made it into a single white blood cell. ''And 60,000 nanoparticles is still not a lot of zinc,'' he said. ''It's a tiny, tiny number, especially seeing as the cells are able to break them down.''
Within 24 hours the cells were able to break down 50 to 60 per cent of the nanoparticles, with most of the remaining particles in the process of decomposition.
Once the particles were in the immune cells, the research team observed them as they deteriorated by shaving off thin layers of the cell and re-imaging the cell as they went. The high-resolution images showed the immune cells were breaking down nanoparticles as they moved deeper into the cell. Dr James said, in the study, the nanoparticles did not reach the cell nucleus.
Results published in the journal ACS Nano found the immune system did what it should: it broke down the nanoparticles before they could enter the bloodstream.
Cancer Council Australia chief executive Ian Olver said the results should reassure those concerned about nanoparticles in sunscreen.
''This research shows us further evidence that the nanoparticles in sunscreen are unlikely to cause harm to beachgoers - unlike the sun's damaging UV rays, which we know lead to higher rates of skin cancer and skin damage.''