Nature of ultraviolet radiation and its sources
Ultraviolet radiation (UVR) is electromagnetic radiation with wavelengths shorter than visible light. Depending on its origin, ultraviolet radiation is classified into natural and artificial. The Sun serves as the natural source, from which UV-A and UV-B ranges reach the Earth's surface, whereas the shortest-wavelength and most biologically aggressive UV-C is normally completely absorbed by the stratospheric ozone layer.
Artificial UVR is generated by specialized equipment—germicidal lamps, quartz irradiators, phototherapy devices—and is widely used in medicine, industry, and sanitation. Both an excess and a deficiency of ultraviolet radiation are unfavorable for the organism: the former leads to tissue damage, while the latter results in ultraviolet deficiency (rickets, vitamin D hypovitaminosis, reduced immune resistance).
Ozone-forming and germicidal effects
The ozone-forming effect lies in the fact that ultraviolet radiation acts as a catalyst for the reaction of ozone formation from molecular oxygen. The resulting ozone is used for disinfecting drinking water and wastewater, as well as for decontaminating and sterilizing medical instruments.
The germicidal effect is the ability of UVR to destroy microorganisms. Within it, the following are distinguished:
- bactericidal action — the complete destruction of bacterial cells;
- bacteriostatic action — the suppression of microorganism reproduction without their complete destruction.
The mechanism is based on damage to protein structures and genetic material (DNA) of the microbial cell: the formation of pyrimidine dimers blocks replication and transcription, which leads to the death or cessation of division of the pathogen.
Pigment-forming and erythemal effects
The pigment-forming effect manifests as the synthesis of melanin and skin darkening. Two forms of it are distinguished:
- Immediate (direct) pigmentogenesis — instantaneous skin darkening without preceding erythema. It is an unfavorable sign: it means that endogenous propigments are insufficient and actually indicates photodamage and skin burn.
- Indirect pigmentogenesis — a physiological tan that appears several hours after irradiation, following the erythema stage. During this time, propigments successfully synthesize in melanocytes, forming a protective tan.
The erythemal effect — skin reddening resulting from vasodilation and improved blood circulation in the irradiated area and adjacent tissues. In medical practice, it is used separately from pigmentogenesis for treating inflammatory, neurological, and trophic disorders (UV therapy in suberythemal and erythemal doses).
Vitamin-synthesizing and bilirubin-lowering effects
The vitamin-synthesizing action is the photochemical conversion of 7-dehydrocholesterol in the skin into vitamin D under the influence of UV-B. Vitamin D is practically the only vitamin whose endogenous synthesis provides a significant contribution to its daily requirement; its deficiency leads to rickets in children and osteomalacia in adults.
The bilirubin-lowering effect consists in the conversion of toxic unconjugated bilirubin into lumirubin — a water-soluble form easily excreted in urine and bile without hepatic glucuronidation. This forms the basis of phototherapy for physiological and pathological hyperbilirubinemia in newborns: the infant is placed under ultraviolet or combined lamps, which ensures a decrease in bilirubin levels and the elimination of yellow skin discoloration.
Adverse effects of UVR
Excessive ultraviolet exposure is accompanied by a number of pathological effects.
- The carcinogenic effect is the induction of malignant neoplasms in irradiated tissues. Target organs include the skin (squamous cell carcinoma, basal cell carcinoma, melanoma) and the visual system.
- The keratogenic effect is inflammation of the cornea (photokeratitis, "electroophthalmia") that occurs when working with welding equipment, in high-altitude regions, or on snow. The visual system is among the structures most vulnerable to UVR.
- Skin photoaging, immunosuppression, exacerbation of photodermatoses.
Prevention includes dosing ultraviolet irradiation, using protective eyewear, photoprotective agents, and complying with hygienic standards when working with artificial UVR sources.
Key points
- UV-C is completely blocked by the ozone layer; UV-A and UV-B reach the Earth's surface.
- UVR catalyzes the formation of ozone, which is used for disinfecting water and instruments.
- The germicidal effect is realized through damage to microbial DNA and proteins and is subdivided into bactericidal and bacteriostatic.
- Direct pigmentogenesis without erythema is a sign of photoburn; a physiological tan develops several hours after erythema.
- The erythemal effect is used in physiotherapy to improve local blood circulation.
- UV-B ensures the synthesis of vitamin D from 7-dehydrocholesterol in the skin.
- The bilirubin-lowering effect underlies the phototherapy of neonatal jaundice through the formation of lumirubin.
- Excess UVR is carcinogenic to the skin (melanoma) and causes keratitis of the visual system.