Ultraviolet radiation represents that portion of the spectrum between X-rays and visible light. The greatest natural source is the sun, which makes sunlight is a broad-spectrum destroyer of large molecules. The ozone layer in the earth's atmosphere screens out much solar ultraviolet radiation; but thermal and chemical pollution of the atmosphere diminishes its screening ability, thus exposing the biosphere to a potential hazard of global extent.
UV radiation causes sunburn and skin cancer and accelerates skin ageing. Overexposure to UV radiation can lead to inflammations of the cornea and the conjunctiva in the eye and causes or accelerates cataract development. It may reduce the effectiveness of the immune system.
The sun emits energy in the forms of light and heat. The light energy is called ultraviolet radiation (UV rays) and it ranges in intensity. We measure UV light in nanometers of wavelength. There are three types of UV rays: UVC, UVB and UVA:
Many people in industrialized countries are exposed to additional ultraviolet radiation because of their use of a wide range of apparatus in homes, industries, places of entertainment, health clubs and research establishments. Typical apparatus emitting ultraviolet radiation includes therapeutic lamps, sterilization and welding equipment. An increase in popular outdoor activities and changed sunbathing habits often result in excessive UV exposure. Skin cancer has frequently been reported in people whose recreation or occupation requires them to be exposed for long periods to direct solar radiation. Occupational exposure to ultraviolet radiation occurs constantly in arc welding and in the use or proximity to a large variety of testing and quality control machines using ultraviolet radiation, in industries as varied as food processing and machine assembly. Other occupational exposure occurs among attendants at health spas, beauticians and similar places where sun lamps are used. Such radiation mainly affects the eyes, causing intense conjunctivitis and keratitis (welder's flash). Symptoms are redness of the eyes and pain, which usually disappears in a few days. No permanent disability appears to result from this occupational disease; however, during periods of eyesight impairment, driving and other accidents may be caused.
Suntan parlour tanning beds, which deliver about 99% UVA to the skin, present a significant danger to users. A 1994 study found that young women aged 18 to 30 who went to a suntan parlour 10 times or more a year had seven times the incidence of melanoma than women who did not go to suntan parlours. The increase in risk for those who use tanning beds occasionally was 3 times.
The market for protective suntan creams in the UK in 1986 was £37 million.