![]() Other UV sourcesĪ number of artificial sources have been devised for producing UV radiation. ![]() The risk for the deadliest form of skin cancer, called melanoma, doubles for someone who has received five or more sunburns, according to the Skin Cancer Foundation. People who get sunburned repeatedly are at much higher risk. The result is skin cancer, the most common form of cancer in the United States. "The UV light causes random damages in the DNA and DNA repair process such that cells acquire the ability to avoid dying," said Chuang. Sometimes the cells with DNA mutated by the sun's rays turn into problem cells that don't die but keep proliferating as cancers. Usually within half a day of overindulging in the sun, the characteristic red-lobster look of a sunburn begins to make itself known, and felt. The body senses this destruction and floods the area with blood to help with the healing process. UV rays can damage the DNA in the body's cells. When this happens, a toxic reaction occurs, resulting in sunburn. However, continued exposure to UV radiation can overwhelm the body's defenses. "Melanin is a natural sunscreen," Gary Chuang, an assistant professor of dermatology at Tufts University School of Medicine, told Live Science in a 2013 interview. When the body senses sun damage, it sends melanin into surrounding cells and tries to protect them from sustaining more damage. Melanin absorbs UV light and dissipates it as heat. This consists of a pigment called melanin, which is produced by cells in the skin called melanocytes. Essentially, a suntan results from the body's natural defense mechanism kicking in. Still, "broad-spectrum ultraviolet radiation is the strongest and most damaging to living things," according to the NTP's "13th Report on Carcinogens." SunburnĪ suntan is a reaction to exposure to harmful UVB rays. No measurable UVC from solar radiation reaches the Earth's surface, because ozone, molecular oxygen and water vapor in the upper atmosphere completely absorb the shortest UV wavelengths. Of the solar UV energy that reaches the equator, 95 percent is UVA and 5 percent is UVB. However, only about 10 percent of sunlight is UV, and only about one-third of this penetrates the atmosphere to reach the ground, according to the National Toxicology Program (NTP). Most of the natural UV light people encounter comes from the sun.
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