Studies show that UVA radiation damages the DNA in human melanocyte cells, causing mutations that can lead to melanoma. Melanocytes darkens the skin to protect it from ultraviolet rays of the sun. "For the first time, UVA rays have been shown to cause significant damage to the DNA of human melanocyte skin cells," says Moon-shong Tang, PhD, professor of environmental medicine, pathology and medicine at NYU School of Medicine. "And because melanocytes have a reduced capacity to repair DNA damage from UVA radiation, they mutate more frequently, potentially leading to the development of melanoma."
In humans, prolonged exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye, and immune system. UVA, UVB and UVC can all damage collagen fibers and thereby accelerate aging of the skin. The Sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, but because of absorption in the atmosphere's ozone layer, 99% of the ultraviolet radiation that reaches the Earth's surface is UVA.