NANOSIZE SUNBLOCK: Although more health and safety studies need to be done, nanosize particles of zinc oxide and titanium dioxide may be the most effective forms of sunblocks. Image: ©ISTOCKPHOTO.COM/BRANISLAV OSTOJIC
Sunscreens shield human skin with chemicals that either absorb or deflect damaging ultraviolet rays, most often titanium dioxide or the zinc oxide known best as the white stuff lifeguards slather on their noses. But it seems they (and others) don't have to put up with the white mess: Zinc oxide can be made clear—and remain just as, if not more, effective as a sunblock—by shrinking it into tiny particles between one and 100 nanometers. (A nanometer equals one billionth of a meter, or 3.94 x 10-8 inches—roughly half the size of a strand of DNA.)
While ideal for image-conscious sun worshippers, however, some environmentalists charge that more research is needed to rule out potential health and environmental risks of reducing chemicals to nanoscale proportions, which can dramatically alter their physical properties. Pencil lead, for instance, becomes stronger than steel when reduced into nanosize atomic clusters.
The question is: "How can something that is so innocuous at bulk size become such a devil at small size," says neurotoxicologist Bellina Veronesi of the Environmental Protection Agency (EPA).
Concerned about such ambiguity, the environmental group Friends of the Earth in Washington, D.C., has called for a ban on use of nanoparticles in sunscreen pending further study, citing results of a survey it conducted of sunscreen manufacturers released this week.
Of the 128 companies surveyed, only 38 agreed to participate; of that number, just nine said they did not use nanoparticles in their sun salves. "The biggest fear is that any time you reduce something to nanoscale, you are really dealing with a whole new set of rules for reactivity that we really don't understand right now," says Ian Illuminato, Friends' health and environment lobbyist who conducted the survey. "There [are] just not enough studies to give us confidence that this is not going to hurt people."
Veronesi, who studies nanosize titanium dioxide, found that it had no effect on mouse brain cells in vitro, but did affect microglia (specialized immune cells) from the animals' nervous systems. At a concentration of just 10 parts per million, photoactive titanium dioxide nanoparticles infiltrated the microglia and caused them to produce free radicals—charged oxygen particles—that are protective in the short term but wreak havoc when continuously released, because they stress healthy cells.
But Veronesi points out that the nanoparticles she studied are not the ones that would most likely be used in a sunscreen. She studies photoactive titanium dioxide, nanoparticles proposed to be used to help break down chemical contamination in polluted areas by enhancing sunlight's effects. Sunscreen manufacturers are more likely to use coated nanoparticles of titanium dioxide, she says, designed to deflect sunlight. "I would imagine that [company] scientists would not want to use a photoactive product," Veronesi says. "That would be a mistake because you are then coating your skin with a nice layer of free radical generating stuff."
Further, it is not clear how nanosize titanium dioxide or zinc oxide could pass from the skin to organs such as the liver or brain where they might do damage. Of 15 scientific studies conducted by government, industry and independent researchers over the past decade, only one found that nanoparticles were absorbed by the skin of rabbits; none detected human skin penetration, even with an electron microscope.
Nevertheless, the finding shows how compounds that are innocuous at larger sizes may reveal a dark side when nanoscaled. And Friends of the Earth complains there have not been enough studies conducted to assess how nanoparticles interact with other chemicals in various sunblocks. "It is jumping the gun to say that nanoparticles cannot penetrate the skin," Illuminato argues. At the very least, he says, manufacturers should be required to label products that contain nanoparticles.