The invigorating properties of sunlight have been promoted by the ancients and by modern health seekers, but the adverse reactions produced or evoked by ultraviolet energy are very diverse and their incidence depends on the specific clinical picture. Many photosensitive factors are involved in skin diseases and can cause aggravating lesions in the epidermis, even causing serious risks such as cancer; and high rates of sun exposure emit a wide range of electromagnetic radiation, but the most important from the dermatological point of view are those belonging to the photobiological spectrum because they cause skin lesions (photodermatosis). In general, they seem to be increasing notably in the last few years all over the world, due to the trend of environmental modifications caused by pollution, and it is now one of the main or most consulted public health problems in the world.