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In page Light therapy:

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Ultraviolet light causes progressive damage to human skin and erythema even from small doses.[1][2] This is mediated by genetic damage, collagen damage, as well as destruction of vitamin A and vitamin C in the skin and free radical generation. Ultraviolet light is also known to be a factor in formation of cataracts.[3][4] Ultraviolet radiation exposure is strongly linked to incidence of skin cancer.[5][1][6]