While I’ve had my reservations about the anti-nanoscreen campaigning, it is important to remember that safety research into the use of nanoparticles in sunscreens is ongoing. A new piece of research on nanoscale zinc oxide and sunscreens has been performed at the Missouri University of Science and Technology and this is something I would put under the category of interesting, possibly disturbing, and not at all definitive.

From the May 8, 2012 news item on Nanowerk,

… researchers at Missouri University of Science and Technology are discovering that sunscreen may not be so safe after all. Cell toxicity studies by Dr. Yinfa Ma, Curators’ Teaching Professor of chemistry at Missouri S&T, and his graduate student Qingbo Yang, suggest that when exposed to sunlight, zinc oxide, a common ingredient in sunscreens, undergoes a chemical reaction that may release unstable molecules known as free radicals. Free radicals seek to bond with other molecules, but in the process, they can damage cells or the DNA contained within those cells. This in turn could increase the risk of skin cancer.

…

“Zinc oxide may generate free radicals when exposed to UV (ultraviolet) sunlight,” May [sic] says, “and those free radicals can kill cells.”

Ma studied how human lung cells immersed in a solution containing nano-particles of zinc oxide react when exposed to different types of light over numerous time frames. Using a control group of cells that were not immersed in the zinc oxide solution, Ma compared the results of light exposure on the various groups of cells. He found that zinc oxide-exposed cells deteriorated more rapidly than those not immersed in the chemical compound. Even when exposed to visible light only, the lung cells suspended in zinc oxide deteriorated. But for cells exposed to ultraviolet rays, Ma found that “cell viability decreases dramatically.”

I categorized this research as mildly disturbing for a couple of reasons. (a) It’s never good to hear about lung cells deteriorating. (b) I never slather sunscreen on my lungs. (c) Why didn’t the researcher test skin cells? (d) The cells were immersed in a solution; what concentration of zinc oxide nanoparticles were present in the solution and is that the same concentration found in my sunscreen?

As the researcher notes this work is just part of a longer scientific inquiry (from the May 8, 2012 news item),

Ma’s research on zinc oxide’s effect on cells is still in the early stages, so he cautions people from drawing conclusions about the safety or dangers of sunscreen based on this preliminary research.

“More extensive study is still needed,” May says. “This is just the first step.”

For instance, Ma plans to conduct electron spin resonance tests to see whether zinc oxide truly does generate free radicals, as he suspects. In addition, clinical trials will be needed before any conclusive evidence may be drawn from his studies.

In the meantime, Ma advises sunbathers to use sunscreen and to limit their exposure to the sun.

“I still would advise people to wear sunscreen,” he says. “Sunscreen is better than no protection at all.”

I suspect that last comment is an indirect reference to a recent study (mentioned in my Feb. 9, 2012 posting) that found 13% of Australians said they weren’t using any sunscreens due to their fears about nanoparticles in those products.

At this point, nanosunscreens get a very cautious pass given the information at hand.

For anyone who’s interested in how stories about science and risk, specifically concerning nanosunscreens, can get reported, I’d advise a glance at the 2020 Science blog. (Andrew Maynard, Director of the Risk Science Center at the University of Michigan, has been writing on his 2020 blog for years and covered nanosunscreens on more than one occasion.) In his May 3, 2012 posting he recounts his experience trying to refine comments about nanosunscreens and safety as a reporter is getting his story, with quotes from Andrew, to press.

ETA Aug. 17, 2012: I’d forgotten but was recently reminded that lung cells and skin cells are the same base cell until they differentiate themselves at a later stage of development. (I’m sure scientists are silently screaming but that’s my best description of the process.) So, I better appreciate why the researchers used lung cells for their study but my comment remains, I don’t slather sunscreen on my lungs. While the results of the study are interesting, they don’t seem applicable to a real world experience.