Wednesday, July 23, 2008

Who's screening sunscreens?

A while back I wrote about sunscreens here and here. But that was already over a year ago - and as anyone who is confused by he says and she says in science knows - the reports just keep on rolling. Just yesterday the New York Times Science Section published an article by Tara Parker-Pope calling sunscreen safety into question, and based in large part on an Environmental Working Group (EWG) report on the stuff. In short, it seems that the EWG is concerned about chemicals like oxybenzone (or BP-3 )which are absorbed by the blood and can be detected in urine - the problem is - health impacts are unknown (although a recent news article in Environmental Health Perspectives reports that in animal studies BP-3 " effects in liver, kidney, and reproductive organs, and studies by other groups have shown endocrine-disrupting effects,") and some claim EWG's rating system for sunscreens lacks scientific rigor. Either way, there just aren't enough studies - though one would wonder maybe why consumers are allowed to slather products on themselves and their young ones when "there aren't enough data."

According to Parker-Pope, "Of nearly 1,000 sunscreens reviewed, the group recommends only 143 brands. Most are lesser-known brands with titanium and zinc, which are effective blockers of ultraviolet radiation. But they are less popular with consumers because they can leave a white residue." But many of the titanium and zinc sunscreens don't leave a residue, and the reason they don't is that titanium and or zinc in "micronized." In other words - really small - sometimes nanosized.

Those who remember smearing the white stuff on their noses in the summer - most likely were using zinc that scattered not only the undesirable UV light but also visible light (hence the clown effect.) Today's micro or nano zinc
allow visible light to pass through them and so appear clear, while still scattering the sun’s shorter and harmful ultraviolet rays. Cool right?

Maybe. My friend Cal Baier-Anderson, blogging over at Environmental Defense just posted about a study initiated following an "...observation that installers of metal roofs who used these sunscreens inadvertently transferred the product onto the roofs. In places where the workers’ skin had touched the painted metal surfaces, the paint showed accelerated weathering. Why? Because the particular type of nanoscale TiO2 in the sunscreen (the anatase crystal form) is photoactive – when it absorbs UV light, it releases free radicals that speed up the oxidation of the underlying paint."

Cal wondered if the same might happen to our skin - inadvertently accelerating the weathering of our skin just as we are trying to stop any further damage. For more on the topic check out Cal's entry Nano on a Hot Tin Roof (rusted!) and her other entry on nanoproducts and sunscreen Burning Questions.

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