There's No Such Thing as a Safe Suntan
Every time you step outdoors, you are bombarded by ultraviolet (UV) radiation from the sun. UV rays cause the number of free radicals in cells to increase. Free radicals are atoms or molecules that contain oxygen in a highly reactive form. They are the same kinds of compounds that cause iron to rust, stone to crumble, and paint to peel. In living cells, they damage membranes, alter DNA, and interfere with life-sustaining chemical reactions. The visible result is a suntan, which is simply the skin's less-than-adequate way of trying to protect itself from further damage. Over time, the damage adds up, and skin cancer is too often the result.
Two (and possibly three) types of UV radiation damage human skin. UVA (wavelength 320 to 400 nanometers) causes oxygen to combine with the brown pigment melanin in the skin. Melanin is the cause of the tanning response. The rays penetrate deep into the support layers under the skin's surface, causing wrinkles and skin cancers. UVA rays are strongest in summer around midday. UVB rays (280 to 320 nanometers) are strong all day long and all year round. They penetrate less deeply into the skin than UVA, but they are a thousand times more powerful. They cause skin cells to make enzymes that destroy collagen and elastin, the proteins that make skin elastic and supple. UVC rays (200 to 280 nanometers) may be the most dangerous of all. That's because the shorter the wavelength, the more energy the radiation possesses. Experts disagree about whether any UVC radiation filters through the atmosphere to the Earth's surface.
Between 1979 and 1995, deaths from malignant melanoma (the most deadly form of skin cancer) rose in the U.S. At the same time, the death rate from most other forms of cancer was declining. Experts say the best treatment for skin cancer is prevention. That means staying out of the sun whenever possible, applying sunscreens with a SPF (Sun Protection Factor) number greater than 30, and wearing protective clothing. Not just any clothing will do. If light passes through the fabric when it's held up to the sun, the clothing will let UV rays through to the skin. It's important to protect the eyes, too, with sunglasses that block all UV rays.
About the Author
Faith Brynie, Ph D
Faith Brynie holds a B.A. in Biology from West Virginia University and an M.A. and Ph.D in science curriculum and instruction from the University of Colorado. She writes books and articles on science and health topics for children, teens, and non-scientist adults. Some of her books have won awards, including two 'Best Book of the Year' citations from the American Association for the Advancement of Science.