[Health effects of ultraviolet radiation]

Exposure to ultraviolet radiation (UVR) occurs from both natural and artificial sources. The main natural source is the sun. On the other hand, artificial UVR sources are widely used in industry and also used in hospitals, laboratories, etc. because of their germicidal properties. They are even used for cosmetic purposes. UVR can be classified into three regions according to its wavelength: as UVA (320-400nm), UVB (320-280nm) and UVC (280-200nm). The UVC has the greatest health effect on humans among the three. The sun radiates a wide range of spectrum of electromagnetic radiation including the UVR, however the radiation below 290 nm in wavelength does not reach the surface of the earth for effective absorption by the stratospheric ozone layer. As a result, UVR from a natural source consists of only UVA and a part of UVB. On the other hand, artificial UVR sources include UVC region and have serious effects on the human body, especially on the skin and eyes. The health effects of UVR on humans can be beneficial or detrimental, depending on the amount and form of UVR, as well as on the skin type of the individual exposed. It has been acknowledged that a long period of UVR deficiency may have harmful effects on the human body, such as the development of vitamin D deficiency and rickets in children due to a disturbance in the phosphorus and calcium metabolism. Appropriate measures to increase the amount of exposure to UVR, especially to UVB radiation by the use of sun bathing, the exposure to artificial UVR sources, etc. have shown to prevent disease states caused by UVR deficiency. The harmful effects of UVR consist of erythema, sunburn, photodamage (photoaging), photocarcinogenesis, damage to the eyes, alteration of the immune system of the skin, and chemical hypersensitivity. Skin cancer is commonly produced by UVR. In this review, various states of UV from solar radiation and the degree of exposure to UVR are introduced. The benefits and harmful health effects of UVR are discussed in relation to the skin type of humans. The measures of protection from UVR, such as sunscreen preparations, protective clothing against UVR, etc. are also introduced.