Screen Test: Reading the Micro-Fine Print

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Nanoparticles are unpredictable because their small size and high ratio of surface area to volume can produce chemical or physical properties that are very different from their larger counterparts. For instance, once TiO2 nanoparticles enter the bloodstream, they are at risk of infiltrating the brain where they can damage cells, whereas larger micron-sized (millionths of a meter) particles of TiO2 are blocked by the blood-brain barrier, which protects the brain from harmful substances in the bloodstream. Fortunately, the consensus in the scientific community, as demonstrated by a 2006 Australian government literature review on the topic, is that neither TiO2 nor ZO penetrate the skin deep enough to actually enter the bloodstream.

That's not to say that the Food and Drug Administration, which hasn't assessed the safety of nanoparticles, can rest easy on Australia's research. Last May, a coalition of advocacy groups, led by the International Center for Technology Assessment (CTA), petitioned the FDA for nanoparticle toxicity testing and stricter labeling on products that contain nanoparticles. "They have not acted on our petition yet except to form, for the first time, a new committee of FDA staff to look at how they should regulate nanoparticles," says Jay Dee Hanson, CTA program director and member of their nanotechnology team.

Further confusing the issue, some companies use the term "micronized" to describe micron-sized particles, while other companies use it to describe particles that undergo what some dictionaries define as "breaking into very fine particles." Since the FDA has no set definition for the term, some companies misleadingly advertise nano-sized particles as "micronized," which is why it's important to verify particle sizes when you're purchasing a product that contains "micronized" or "nanoparticle" ingredients.

Nano-Free Suggestions

Because the studies present greater evidence against chemical sunscreens, and because it's riskier to spend time outdoors with no sun protection whatsoever, The Green Guide feels that mineral sunscreens are the better alternative, in addition to common-sense measures such as limiting time spent outdoors during peak sun hours and covering up with hats and long-sleeved clothing.

To avoid confusion, we have only included products containing TiO2 and ZO in micron-sized particles (1 micron or larger) or nano-sized particles larger than 100 nm, which are too large to penetrate the deepest skin layers. These are also free of The Green Guide's Dirty Dozen chemicals:

New for '07

Burt's Bees new Chemical Free Sunscreen SPF 15 with TiO2 ($15/3.5 oz.; www.burtsbees.com, 800-849-7112)

Alba Botanica Sun Fragrance-Free Mineral Sunscreen SPF 18 with TiO2 ($9.95/4 oz. bottle, www.albabotanica.com, 877-263-9456).