Photocarcinogenesis & Photoprotection || Ultraviolet Radiation (UVR): An Introduction

摘要： Radiant energy of sun is essential to perform metabolic processes of all flora and fauna on the earth. The electromagnetic radiations (EMR) emitted by sun extend from very long wavelength radiation, such as radiowaves (A ″′ 3 × 108 m), to very short wavelength radiation, such as cosmic rays (A ″′ 3 × 10?19 m). The EMR reaching at the earth surface contains wavelength from 290 to 4000 nm. However, the UV portion covers from 200 to 400 nm. The range from 200 to 400 nm is often arbitrarily categorized into UVA, UVB, and UVC radiation. Solar radiation less than 290 nm does not reach at the earth’s surface due to the presence of O3 layer in stratospheric zone. But, last from few decades due to anthropogenic activities, the concentration of ozone layer decreases on stratospheric zone. As a consequence of that, UVB radiation levels are rising to 1% a year. Thus, the deleterious health effects on human beings (skin aging, cataracts, skin cancer, and immune suppression) are enhanced by UVR.