Ultraviolet Radiation

M. D. Anderson Cancer Center
Date: May 2008

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Dr. Susan Chon, assistant professor of dermatology at M. D. Anderson Cancer Center, speaks about ultraviolet radiation during a lecture on skin cancer prevention.

So, first thing, what is ultraviolet radiation? There's actually three main types, there's UVA, the B and the C and C is really very short. It gets absorbed by the atmosphere, so that's not really dangerous to our skin, but what you see in all the sunscreen labels is UVA and UVB protection and that's important because UVB and UVA both contribute to sun damage, but also formation of skin cancers.

UVB is shorter wavelength and it causes that immediate kind of sunburn and induces skin cancers and UVA causes a lot more allergic reactions and you get a lot more photodamage, meaning photoaging from the sun from the UVA rays.

What else affects how much sun you get? Altitude. So when people go skiing and they're at high altitude, they get more sun damage. The low latitudes is when you travel to the kind of, you know Caribbeans or to any kind of island or more kind of a tropical weather. You're closer to the equator, you're gonna get some more sun.

And also seasonal. Summer months, even in Texas, it's even more intense in the summer and we often feel that versus the winter time. But one thing they've noticed is that in the Sun Belt, the Southern states, the fluctuation is much less than say, Washington State or Oregon. They have much more drastic differences in their seasons. But here in the Sun Belt it's pretty bad all year 'round I have to say.

And one other thing, reflective surfaces, so that if you're outdoors, snow, sand, water, they increase your sun exposure. The only way that water is protective is if you're several meters below -- that's really only diving. Otherwise, you're getting now kind of cooked on all sides with the magnification of the water.

And then what decreases the UV? Cloud coverage helps but I have so many patients who come in say, I got sunburned, but it was a cloudy day. It's because there's still light outside. All those long UV rays go right through the clouds and they're still getting to your skin, so don't feel a false sense of security and say I don't need anything, it's kind of cloudy. You're still gonna get a lot of sun and if it's mid-day sun, you're still gonna get sunburned. And then as I mentioned the underwater thing. Only if you're diving, everyone else you're still getting a lot of sun if you're just gonna go swimming in the water.

And what kind of effects happen when you get sun exposure? Well, everyone's experienced some form of sunburn. And then the delayed effect, or longer time effect is tanning, you also get altered immunity. When the sun, hits your skin it actually changes the immune system of the skin. Photoaging and again, if anyone's thinking about how much sun damage they have, just to look underneath their chin, the skin here or look at your buttocks. That's not sun exposed skin that's very different from your face or the backs of your hands and then of course photocarcinogenesis is you know basically how the sun damage induces skin cancers over decades of your life.

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