Screen Test: Reading the Micro-Fine Print

With Memorial Day right around the corner, we have a lot to look forward to: long, hot days, pool parties, barbecues, baseball games and picnics in the park. But with these outdoor activities comes the very real threat of the sun's dangerous—and deadly—rays: Ultraviolet-B (UVB) rays, known to cause sunburn and associated with an increased risk for basal and squamous cell cancers and melanoma skin cancer, and ultraviolet-A rays which penetrate deeper into the skin, enhancing UVB’s carcinogenic effects.

In fact, approximately 90 percent of all skin cancers are caused by sun exposure, and this year alone, the American Cancer Society estimates that over 1 million Americans will be diagnosed with skin cancer and more than 10,000 will die from it. And atmospheric scientists are concerned that massive Asian sales of air conditioners, which rely on ozone-depleting chemicals, bode ill for the hole in the ozone layer.

That information, coupled with research demonstrating that sunscreen poses its own risks, is reason enough to scrutinize product labels.

Chemical sunscreens that absorb the sun's rays commonly contain compounds that have been shown by numerous studies to interfere with the body's hormonal systems. The most prevalent include benzophenone, homosalate and octyl methoxycinnamate (also called octinoxate). Other chemicals like padimate-0 and parsol 1789 (AKA avobenzone) have the potential to damage DNA once activated by UV rays.

Mineral sunblocks that contain titanium dioxide (TiO2) or zinc oxide (ZO) are preferable to chemical sunscreens, because rather than being absorbed into the skin, the minerals lie on top of the skin, reflecting UV rays before they cause damage. The choice of most lifeguards, these sunblocks are famous for giving off that unattractive "white" mask.

But this is where problems with minerals arise. In order to reduce the visibility of sunscreen, many manufacturers use nanometer-sized particles of TiO2 and ZO. A nanometer (nm) is about a billionth of a meter—a unit so small that a single human hair is about 80,000 nm in diameter. The U.S. government has defined nanomaterials as particles smaller than 100 nm, and according to the Australian government, most nano-sized sunscreens use particles that size or smaller because the sunscreens become transparent on skin.