According to a team of scientists at Australia’s Commonwealth Scientific and Industrial Research Organisation, despite previous research finding that nanoparticles do not penetrate the skin, it remains debatable as to whether this remains true under normal conditions of using sunscreen.
At a Global Nanomaterials Safety workshop in London earlier this month, Dr Maxine McCall showcased her team’s progress on ‘Dermal absorption from sunscreens containing zinc oxide particles’ revealing that two special sunscreens were made especially for a human study whereby one contained nanoparticles of zinc oxide and the other larger (non-nano) particles to determine if there was a dependence on particle size for dermal absorption.
According to Dr. McCall, most in vitro studies to assess dermal penetration of nanoparticles are conducted for a period of up to 24 hours, and that the OECD WPMN is currently assessing whether a number of test guidelines, developed for chemicals, are applicable to nanomaterials.
“Our results imply that longer study periods may need to be considered when assessing dermal penetration and absorption of nanoparticles and we are communicating this information to the OECD WPMN,” the expert told CosmeticsDesign-Asia.com.
The human study involved the team of scientists applying sunscreen twice daily for five days as well as obtaining numerous blood and urine samples before, during, and after the period at the beach.
"The method we used to detect the traceable zinc is highly sensitive," explains McCall.
"The first detection of traceable zinc from ZnO particles in the sunscreens were found in the blood at the end of the second day at the beach and after a total of 4 sunscreen applications, levels continued to increase after sunscreen application ceased," she adds.
The expert went on to further reveal that the blood and urine samples from the females with the sunscreen with nanoparticles had slightly higher levels of traceable zinc than those of the sunscreen with larger particles.
However, Dr. McCall concludes by informing this publication that the total amounts of traceable zinc detected from the sunscreens were very small when compared with amounts of natural zinc normally present in the human body.
SCCS view on the matter..
The EC's Scientific Committee on Consumer Safety recently announced it had reviewed its toxicological evidence and found no evidence that ZnO nanoparticles are absorbed through skin and or via the oral route.
And concluded that the use of zinc oxide nanoparticles, at a concentration up to 25 percent as a UV-filter in sunscreens, “can be considered not to pose a risk of adverse effects in humans after dermal application."
However, it did note that this did not apply to other applications that might lead to inhalation exposure to zinc oxide nanoparticles, such as sprayable products.
“In view of the lung inflammation induced by ZnO particles after inhalation exposure, the use of ZnO in cosmetic products which may result in inhalation, is of concern.”