During action on living organisms, UV radiation is already absorbed by the upper layers of tissues, plants or skin of humans and animals. The biological effect of radiation is based on chemical changes in biopolymer molecules. These changes are caused both by direct absorption of radiation quanta, and (to a lesser extent), by water radicals (HO-; H3O +; H2O2-2) and other low molecular weight compounds formed during irradiation.
Small doses of UV radiation have a beneficial effect on humans and animals – they contribute to the formation of vitamins of group D and improve the immunobiological properties of the body. A characteristic skin response to UV radiation is specific redness – erythema (radiation with a wavelength of 296.7 nm and = 253.7 nm has the maximum erythema effect), which usually proceeds to protective pigmentation – “tanning”. Large doses of UV radiation can cause eye damage (photophthalmia) and skin burns. Frequent and excessive doses, in some cases, can cause a carcinogenic effect on the skin.
In plants, UV radiation, changes the activity of enzymes and hormones, affects the synthesis of pigments, the intensity of photosynthesis and photoperiodic reaction. Large doses are unfavorable for plants, as evidenced by their available protective devices (for example, the accumulation of certain pigments, cellular mechanisms of recovery from damage).
On microorganisms and cultured cells of higher animals and plants, UV radiation is detrimental and causes mutagenesis (more, at a wavelength in the range of 280-240 nm). Usually, the spectrum of lethal and mutagenic effects approximately coincides with the absorption spectrum of nucleic acids – DNA and RNA, in some cases the biological action spectrum is close to the absorption spectrum of proteins. The main role of UV radiation on cells belongs to chemical changes in DNA: pyrimidine compounds, (mainly thymine), during the absorption of UV radiation quanta, form dimers that interfere with the normal doubling (replication) of DNA in preparing the cell for division. This can lead to cell death, or changes in their hereditary properties (mutations).