Most commercial sunblocks are good at preventing sunburn, but they also can seep into the skin's surface and enter the bloodstream, posing health concerns such as the risk of cancer they were designed to prevent.
Now researchers have developed a new kind of sunblock, made with adhesive nanoparticles that stays on the surface of the skin and keeps sunblock compounds out of the body.
These nanoparticles are large enough to keep from going through the skin's surface, and so sticky that they don't even go into hair follicles, which are relatively open, according to Mark Saltzman, lead author on the new report published today in Nature Materials, and professor of biomedical engineering at Yale University.
Saltzman told Discovery News that there is growing concern about the chemicals in sunscreens.
"People have found sunscreen chemicals in urine and breast milk, that suggests it gets into the body and accumulates in several tissues," Saltzman said. "In addition, most sunscreen agents are made with polyaromatic hydrocarbons, the same chemicals that cause cancer in other settings."
The Environmental Working Group, a Washington-based advocacy group, puts out a yearly guide listing which sunscreens are to be avoided because of these possibly toxic chemicals.
Using animal models, the scientists at Yale tested their sunblock against direct ultraviolet rays and their ability to cause sunburn. Even though it used a significantly smaller amount of the active ingredient than commercial sunscreens, the researchers' formulation protected equally well against sunburn, according to the paper.
They also looked at another effect of UV light. When the active ingredients of sunscreen absorb UV light, a chemical change triggers the generation of oxygen-carrying molecules known as reactive oxygen species (ROS). If a sunscreen's agents penetrate the skin, this chemical change could cause cellular damage, and potentially facilitate skin cancer.
"Commercial chemical sunblock is protective against the direct hazards of ultraviolet damage of DNA, but might not be against the indirect ones," co-author Michael Girardi, a professor of dermatology at Yale Medical School, said in a statement. "In fact, the indirect damage was worse when we used the commercial sunblock."
Saltzman said the nanoparticle is comprised of a UV filter surrounded by a ring of water soluble molecules to make them adhesive. The formula however should be easier to apply that some pasty sunscreens, he said.
"I have three-year-old daughter and most of the sunscreens for children are based on zinc oxide," he said. "They are pasty, gritty and hard to apply. This should feel totally different, they will suspect easily in water-based liquids. I could imagine, you could make it into a spray or a gel that would be slippery not greasy."
Saltzman said that his team is now seeking approval to test the formula in human clinical trials and that a product is only several years away.
One expert was impressed by the new study.
"This is a potential game changer," said Eleni Linos, assistant professor of dermatology at the University of California San Francisco. "The scientists have essentially developed a material that allows sunscreens to stay on the skin (where they can protect from UV rays) but not get absorbed. Although there is no strong epidemiological data that sunscreens are dangerous to humans, some of the chemicals are absorbed. The bottom line is that our patients are concerned- and come in with questions about sunscreen safety. This is on a lot of people's minds."
Linos said her recommendations to her patients will remain the same: wear a broad hat, sunglasses, long sleeves, avoid midday sun and seek shade first. Then use a broad spectrum sunscreen for areas still exposed.