Which of the following ultra-violet radiation cause most skin disorder ?

Ans. is `b' i.e., UV-B Ultraviolet radiation (UVR) UVR is electromagnetic radiation with wavelength (200-400 nm) shoer than visible light, but longer than x rays. There are three segments of UVR. 1. UV-C/Sho wave UV-radiation (200-290 nm) It is most dangerous as it has serious effects on the skin. But, It is not medically impoant as it is absorbed by ozone layer and hence does not reach the surface of eah in measurable amounts. 2. UV-B/medium wave UV-radiation (290-320 nm) Medically most impoant UVR as it causes most of the dermatoses, e.g., sunburn, tanning, photoaging. It is absorbed in epidermis. It is used in phototherapy as narrow band UV-B (NBUVB) which has wave length of 311 nm. 3. UV-A/Long wave UV-radiation (320-400 nm) It is absorbed in dermis. It is fuher divided into : ? UVA-2 ---> 320-340 nm UVA-1 ---> 340-400 NM Wood's lamp uses UVA-1(365 NM). UVA is also used in photochemotherapy (PUVA).