Ultraviolet radiation is the part of sunlight between violet (at the edge of visible light) and x-rays. It is responsible for both healthy looking suntans and blistering sunburns. Sunscreen and protective clothing may block ultraviolet (UV) radiation and offer protection from sunburns and skin cancer, but some UV rays are beneficial, and even essential, in small amounts.
Sunlight - boon or bane?
Ultraviolet Radiation
Ultraviolet light is invisible and of a shorter wavelength than the visible light spectrum. The shorter the wavelength of light, the more harmful its effects. According to the World Health Organization (WHO), prolonged "exposure to solar UV radiation may result in acute and chronic effects on the skin, eyes and immune system." These effects range from simple sunburn to cataracts to malignant melanoma skin cancers. UV radiation that affects biological forms falls into three categories.
UVA
The longest-wavelength UVA rays penetrate deeper into the skin and cause premature skin aging, wrinkling and cataracts. According to WHO, "recent studies strongly suggest it may also enhance the development of skin cancers." Of the total amount of UV radiation we receive, UVA accounts for about 95 percent of it.
UVB
Shorter-wavelength UVB rays are stronger but do not penetrate beyond the superficial layers of skin. However, this radiation causes skin to burn and age and, according to Jeannie Allen of NASA's Earth Sciences Division, suppresses parts of the immune system and causes mutations in DNA, inducing skin cancer. Only about 10 percent of total UVB radiation penetrates through the ozone layer of the atmosphere, though thinning of the ozone layer since the mid-1970s has allowed more radiation to pass through.
UVC
Shorter than either UVA or UVB, "UVC is almost never observed in nature because it is absorbed completely in the atmosphere," according to certified health physicist Dr. Gary Zeman. UVC radiation is used safely for industrial purposes, however, as a disinfectant or germicide to kill or inactivate bacteria and other microorganisms in fluids, air or on the surfaces of solids.
Beneficial Effects of UV Radiation
Ultraviolet radiation is necessary for the production of vitamin D in the body. Vitamin D is essential to maintaining bone health in both children and adults. It may also play a role in preventing certain types of cancer, such as prostate, colon and breast cancer. According to the National Institute of Health's Office of Dietary Supplements, vitamin D is found in very few foods naturally, though some foods are fortified with vitamin D. Most people meet their need through sun exposure. People with limited sun exposure are at a risk for vitamin D deficiency.
A Quandary
Some experts say prudent sun exposure is the best way to protect health. According to the Mayo Clinic, as little as 10 minutes a day of sun exposure can be enough to prevent vitamin D deficiency. Yet the position of the American Academy of Dermatology is that "vitamin D should not be obtained from unprotected exposure to ultraviolet radiation." The Academy believes supplements and fortified foods are a better answer in order to minimize the risks of skin cancer.
Tags: skin cancer, about percent, immune system, ozone layer, Radiation Ultraviolet
