Thursday, February 24, 2011

How Much UV Radiation Does Snow Reflect?

Over the coming weeks, days will get warmer, the sun will rise higher in the sky, and backcountry enthusiasts will be out romping in blissful, snowy spring conditions. But consider this: Snow reflects up to 80 percent of UV radiation, which means that your UV dose is close to double what it would be otherwise. (By comparison, grass, soil, and water reflect less than 10 percent; dry beach sand 15 percent; and sea foam 25 percent, according to this UV fact sheet from the World Health Organization.) On top of that, UV exposure also increases by approximately 10 percent for every 1,000 feet of elevation gain.

All that reflected UV radiation is also hitting your body from below, which means that your entire head and face are getting UV exposure. This includes areas normally protected from top-down UV exposure, including the underside of your nose, chin, even the backs of your ears. I've even heard of extreme cases where mouth-panting mountaineers get sunburn on the roof of their mouths from reflected light. And don't forget the increased UV exposure to your eyes; prolonged exposure to high UV levels leads to snow blindness.

So what's the upshot? Lather up with a high-powered sunscreen if you're headed out into the snowy backcountry—and don't be deceived if temperatures are cold or the wind is blowing. Neither has any effect on UV. Make sure to cover the undersides of your nose, chin, and ears. And always have a pair of sunglasses or goggles on hand.

I find the nose the most problematic, especially since it tends to run in cool conditions and all that snot-wiping rapidly removes the sunscreen as well. To combat this, I always carry a high-SPF lip balm and regularly apply it to both my lips and nose. Make sure it's a scent that you like!

For more information on sunscreens and UV exposure, check out my recent article Code Red: Pale is the New Tan.

Equipped” is an AMC Outdoors blog, written by Matt Heid.

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