Gwyneth K. Shaw Photo
Sunscreens with super-small versions of physical sunblockers are often labeled as “natural.”
With sunscreen season approaching, new questions have emerged about the safety of ultra-tiny particles that are becoming a common ingredient.
But barring hard evidence of danger, experts — including scientists studying sunscreen safety — have the same advice this summer: Don’t let fear stop you from protecting yourself.
Buying sunscreen has become the adventure before the summer vacation. Should you go with a traditional lotion containing oxybenzone? Or should you choose a “mineral” sunscreen made with nano-sized titanium dioxide or zinc oxide? Some studies suggest either choice might be problematic down the road.
The important thing, experts say, is that you use a sunscreen, regardless of its recipe. Also, stay out of the sun as much as possible, and wear hats and light clothing to minimize sun exposure.
“At this point, I would say, if you go out in the sunshine, you use suntan lotion,” said Yinfa Ma, a chemistry professor at Missouri University of Science and Technology. “You have to protect yourself.”
Nanotechnology is a broad term that encompasses a wide variety of uses of very small materials (a nanometer is a billionth of a meter). These substances can make better batteries or lighter and stronger bike frames, as well as new medical instruments and medicines that can save lives. They’re increasingly common in consumer products, from sunscreens to stain-repellent pants to boat paints that resist algae growth.
Nanomaterials are believed to hold great promise for a wide variety of applications. Their ultra-tiny size also gives them different properties; scientists are struggling to figure out whether that can make them dangerous in the process, and how and why it happens.
Sunscreens with nanoparticles are increasingly popular. The super-small particle size allows physical sun blockers like zinc oxide and titanium dioxide to disappear on the skin, ending the white stripes of years past. They’re marketed as “all-natural,” to capitalize on the growing concerns about other sunscreen ingredients, including oxybenzone and retinyl palmitate, a form of Vitamin A.
However, these newfangled formulas aren’t labeled as “nano” anything, leaving it to the consumer to figure it out.
Ma has studied several nanoscale metallic oxides, looking for clues about their safety. Working with a graduate student, Ma found evidence that nanoscale zinc oxide releases free radicals when exposed to sunlight. Free radicals can damage cells, which may lead to cancer.
Ma’s study was on lung cells, not human skin, so it’s unclear just how indicative these results are of nanoscale zinc oxide’s overall effect.
Another researcher, Brian Gulson of Australia’s Macquarie University, applied sunscreen to people, then studied their blood and urine. When he and his colleagues published findings two years ago that zinc in the sunscreen makes its way into the blood—albeit at incredibly small levels — it was big news.
Gulson recently published results from the pilot project done ahead of the larger study, which reflect similar findings.
“I don’t think it is an issue for most uses which are generally, say, for a holiday of a few weeks or intermittent use at the weekend,” Gulson said in an email.
The Environmental Working Group, an advocacy group that issues an annual sunscreen guide (click here for this year’s version), rates the metal oxide sunscreens as preferable to those with other ingredients, Gulson said.
“I feel more comfortable applying these — if I need to,” he said, adding that he rarely spends much time in the sun outside what’s needed to soak up adequate Vitamin D.
Gulson said his studies do raise some questions, including whether these nano-based sunscreens are safe for workers who might apply them every day for years, and how they interact with children’s skin. The latter is an issue for a broad swath of products, including drugs, since products are rarely tested on human kids because of ethical and other issues.
But zinc is an essential nutrient for people, Gulson said, so perhaps minuscule amounts of nanoscale zinc oxide being absorbed through the skin isn’t a big deal.
The U.S. Food and Drug Administration, which regulates sunscreens as over-the-counter drugs, issued new labeling guidelines last summer, but says it’s still studying nano-based sunscreens. Some consumer and environmental advocates have called for companies or regulators to take nanoparticles out of sunscreen — or, at least, label them — until there is concrete evidence that these substances aren’t harmful.
Several FDA researchers published a study using pig skin that found no absorption of nanoscale titanium dioxide. Gulson called the FDA study “excellent,” but added, “pig skin is not human skin.”
Titanium dioxide and zinc oxide work the same way as sunscreens — by physically blocking the sun’s rays — but are obviously different chemically, making it difficult to extrapolate information about one’s characteristics from studies of the other.
Ma is in the process of submitting a follow-up to the original paper, published in 2009, and plans to continue testing, including on human skin.
“To comprehensively evaluate sunscreens which contain zinc oxide, much more study must be done to draw a conclusion,” he said.
He also wants to scrutinize the other ingredients in these sunscreens, to determine whether some of them might mitigate the free radicals that appear to be created by the zinc oxide.
“Maybe other chemicals can help by minimizing the effect or by absorbing the free radicals, maybe not. I don’t know,” he said. “This is maybe something for the [sunscreen] companies to think about.”
In the meantime, advocates urge consumers to use sunscreen — although they differ about which ones. In its annual pre-Memorial Day press release, the American Academy of Dermatology declared sunscreens with oxybenzone, retinyl palmitate and nanoparticles safe and effective.
The Environmental Working Group is more cautious, rating nano-based sunscreens as preferable if they don’t contain other substances the group labels as problematic.
Everyone offering advice stresses that sunscreen is a tool for lowering the risks of sun exposure, not a cure-all. Gulson said many people make the basic mistake of not applying enough sunscreen to get the protection level touted on the bottle. That could be as much as half a tube of lotion for an adult, he said, a standard few of us meet.
Stay out of the sun during peak hours, stay in the shade when possible, and wear sunglasses too.
“We recommend — as does the Environmental Working Group (EWG) and our Cancer Councils — people continue to use sunscreens until the potential problem of nanoparticles in cosmetics is resolved,” Gulson wrote. “As skin cancer is not a pleasant alternative.”
Click here for more Independent articles on nanotechnology.