Sunscreen labels do not have to say if they contain nanoparticles in Australia.
Credit: iStockphoto
SYDNEY: Zinc from sunscreens can penetrate healthy adult skin, according to two Australian studies. The results raise questions over the safety of sunscreens containing zinc oxide nanoparticles – which may be dangerous in the body if still in a nanoparticle form.
Zinc oxide and titanium dioxide block UV light across a wide spectrum of wavelengths, making them suitable for use in sunscreens. Sunscreens containing large bulks of these particles of the metal oxides reflect light and appear white on the skin, and so they are not popular with consumers.
Many sunscreens for sale in Australia now contain nanoparticles of zinc oxide and titanium dioxide, measuring just 20 to 30 billionths of a metre across. The nanoparticles don't reflect sunlight, making the lotion appear clear when rubbed into the skin.
While such particles have the potential to cause damage to DNA and cells, scientists have been unsure until now whether the particles were penetrating through the skin.
Zinc gets into the bloodstream
Now new research shows that zinc from the sunscreens reaches the bloodstream, said geochemist Brian Gulson from Macquarie University at the International Conference on Nanoscience and Nanotechnology (ICONN) in Sydney last week.
Having zinc in the bloodstream is not necessarily dangerous - especially as the amount they found was much smaller than the recommended daily dietary intake for zinc.
"The amounts we are seeing compared to the amount in blood are really quite tiny," said Gulston. "It's a thousand times lower than what's actually floating around in our bodies."
He suggested that until more is known about skin penetration of the metal oxides that we continue to follow the Cancer Council’s advice of slip, slop slap.
Blood and urine samples show zinc gets in
In the experiment, the researchers concocted two types of sunscreen zinc oxide, using a rare non-radioactive isotope of zinc, zinc-68, which has four more neutrons than common zinc 64. One sunscreen contained 'nano' particles of zinc oxide and the other contained 'bulk' particles at least five times larger.
Test volunteers were separated into two groups and applied sunscreen twice daily: one group used sunscreen with bulk particles and the other used sunscreen with nanoparticles.
Gulson's team then took blood and urine samples from volunteers to see whether levels of zinc 68 increased compared to levels measured before the test.
