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UV radiation: friend and foe

June 30, 2012
(Ricardo DeAratanha / Los…)

The sun does lots of cool stuff. We couldn't live on Earth without it. But the havoc it wreaks with our skin is not so hot.

The culprit is ultraviolet, or UV, radiation, which can actually be very useful in fluorescent lighting and sterilizing medical equipment, or by stimulating our bodies to make vitamin D.

But a little goes a long way, and overexposure to UV radiation is a major cause of skin cancer. (It's classified as a human carcinogen by the U.S. Department of Health and Human Services and the World Health Organization.) It can also suppress the immune system, harm the eyes and make skin old before its time.

UV radiation comes in three main types: UVA, UVB and UVC. Since most UVC rays get absorbed by the ozone layer, all we have to worry about for now (as long as we have an ozone layer) are UVA and UVB rays.

UVA rays, which comprise as much as 95% of the UV radiation that makes it to Earth, have a longer wavelength than UVB rays and go deeper into the skin. They can also go through clouds and glass. While they deserve a lot of the blame for crinkling us up, they also earn most of the credit for giving us the tans we often crave. In fact, UVA rays are the mainstays in tanning booths, which emit doses up to a dozen times that of the sun.

For years, scientists let UVA rays off the hook for cancer, but no longer. Research has now shown that UVA damages skin cells called keratinocytes, two types of which are the basal and squamous cells that have each given their name to a common kind of skin cancer.

Sad to say, even a gorgeous tan is a sign of skin damage caused by UVA rays, and damage adds up with repeated tanning and can eventually lead to skin cancer. Basal cell and squamous cell cancers are especially common among frequenters of tanning booths.

While UVA rays tan us, UVB rays burn us. Worse yet, they're stars at instigating skin cancer. On the plus side, they're less multitudinous than UVA rays, their role in skin aging is modest and they can't make much of an entrance through glass.

—Karen Ravn

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