Summary
Highlights
Ultraviolet (UV) radiation is part of the electromagnetic spectrum, located beyond white light. It's classified into UV-A, UV-B, and UV-C based on wavelength and action. UV-A (390-315 nm) is 'proximal', UV-B (315-280 nm) is 'intermediate', and UV-C (280-185 nm) is 'short wavelength'. UV-A and UV-B have therapeutic applications, while UV-C is used for sterilization.
Various sources produce UV radiation, including carbon arc lamps, mercury vapor lamps, inverse U-shaped tubes, filament lamps (most common), Wood's lamps, and 'Corona Mayor' lamps. Filament lamps, especially tungsten filament lamps, are similar to infrared lamps but differ in power and use a quartz filter. This filter reduces white light while allowing UV radiation to pass through, and these lamps operate at very high temperatures, requiring cooling time between uses.
UV radiation's local effects include erythema, a reddish coloration. Initially, any redness is due to infrared radiation; true UV-induced erythema is delayed, appearing 24-48 hours later. It also increases melanin production, leading to darker skin pigmentation, and accumulates carotenes in fat.
General effects include increased red blood cells, bactericidal action (useful for skin lesions), increased platelets for healing, histamine release, and peripheral vasodilation (an indirect effect). UV also lowers arterial blood pressure and converts provitamin D into vitamin D, aiding calcium fixation, which gives it anti-rachitic properties. It increases blood calcium levels and optimizes oxygen utilization in tissues.
Erythema is categorized into four types. Erythema 1 (tonic dose) is a delayed redness without scaling or pigmentation, the desired outcome for treatment. Erythema 2 (stimulating dose) causes more intense redness, like a sunburn, with slight pigmentation and scaling (skin peeling), and itching. Erythema 3 (inflammatory dose) is a much more intense sunburn, causing significant pigmentation, extensive scaling, itching, and edema. Erythema 4 (destructive dose) results in very intense, long-lasting redness, deep and permanent pigmentation, blisters (containing water or pus), and necrotic cellular lesions that do not heal but leave scars.
UV radiation dosage depends on skin phototypes, which classify skin types based on their reaction to UV. Type 1 (white skin) always burns and never tans. Type 2 (white skin) always burns but tans minimally. Type 3 (white skin) burns minimally but tans gradually. Type 4 (brown skin) burns minimally and tans well. Type 5 (dark brown skin) rarely burns and tans perfectly. Type 6 (darkest brown skin) never burns and tans perfectly, achieving a permanent dark hue.