Ultraviolet rays have a very high energy. In this regard, significant changes occur in the process of their absorption in molecular and atomic structures. The absorbed energy emitted by ultraviolet rays can be used to break the weak bonds of protein molecules. This process is called photolysis. Its course is accompanied by the release of active substances under the influence of medium-wave ultraviolet radiation.
Short-wave exposure provokes the denaturation of protein polymers, which, losing their activity, precipitate. Ultraviolet rays have a special effect on DNA molecules. In the process of influence, there is a violation of DNA doubling and cell division. Along with this, ultraviolet rays cause oxidative degradation in protein structures. This leads to cell death. But damaged nuclei have the ability to repair (dark repair). This is possible under the influence of long-wave UV radiation and the energy of visible light. Certain enzymes are involved in these processes.
Dark and photoreactive repair are classified as protective and adaptive reactions. They are laid down by nature in the human body and provide protection against the effects of UV radiation.
Medium-wave exposure promotes the formation of vitamins. So, ultraviolet rays convert the provitamins contained in the skin into vitamin D. Penetrating only one tenth of a millimeter, the effect provides the formation of a large amount of energy in comparison with other electromagnetic vibrations of the infrared and visible spectrum.
Photolysis and denaturation occur in a spiky layer of the skin. Along with this, histamine, acetylcholine, and biogenic amines are released. These compounds provoke the development of erythema. It occurs after 2-8 hours. Protein decay products contribute to vasodilation, leukocyte migration, and skin edema. All these phenomena are complicated by irritation of skin receptors, receptors of internal organs, with the occurrence of neuroreflex reactions. Decay products disperse through the bloodstream, exerting a humoral effect. Ultraviolet irradiation of the mid-wave spectrum provokes an aseptic inflammatory reaction in the skin. By the second day, it reaches its maximum. On the seventh-ninth day, an inflammatory reaction passes, instead of it a tan appears. Short-wave radiation provokes erythema faster, while leaving poorly expressed pigmentation.
The maximum pigment-forming effect is exerted by long-wave UV rays. Melanin is formed in melanoblasts located in the basal layer of the epidermis from tyrosine, products of adrenaline decomposition and dioxiphenylalanine. Its (melanin) giant molecules prevent fragments of protein molecules destroyed by UV radiation from penetrating deep into the dermis. In addition, melanin molecules absorb infrared rays and the visible spectrum. Thus, the skin is protected from overheating and burns. In areas affected by ultraviolet rays, the lymph flow and blood flow increase, the regeneration of the cover improves, and the synthesis of collagen fibers increases. With intensively occurring erythema, chronic and acute inflammatory processes intensify.
Ultraviolet exposure is widely used in cosmetology. So, in the tanning bed get an even and beautiful tan. In this case, long-wave rays are used, and filters are used for short-wave and medium-wave radiation in tanning salons.
It should be noted that excessive exposure to the sun can lead to premature aging, lowering the elasticity of the skin. In addition, the formation of free radicals that contribute to the oncology can be activated.
An ultraviolet index is used to determine the distinction between a "harmful" and a "useful" sun. This parameter signals the level of radiation on Earth.