BACKGROUND: The sun is a natural source of UV radiation. It can be divided into three bands, UVA (315-400 nm), UVB (280-315 nm) and UVC (100-280 nm), where the radiation up to 290 nm is very effectively eliminated by the stratospheric ozone. Although UV radiation can have a beneficial effect on our organism and can be used in the treatment of several skin diseases, it must primarily be considered harmful. METHODS: In the presented work, we focused on the study of the longer-wavelength UV components (UVA and UVB) on the human epidermal keratinocyte line HaCaT. As UVA and UVB radiation sources, we used commercially available UVA and UVB tubes from Philips (Philips, Amsterdam, The Netherlands), which are commonly employed in photochemotherapy. We compared their effects on cell viability and proliferation, changes in ROS production, mitochondrial function and the degree of DNA damage. RESULTS: Our results revealed that UVB irradiation, even with significantly lower irradiance, caused greater ROS production, depolarization of mitochondrial membrane potential and greater DNA fragmentation, along with significantly lowering cell viability and proliferative capacity. CONCLUSIONS: These results confirm that UV radiation causes severe damages in skin cells, and they need to be protected from it, or it needs to be applied more cautiously, especially if the component used is UVB.

Department of Medical Biophysics Faculty of Medicine and Dentistry Palacky University in Olomouc Hnevotinska 3 775 15 Olomouc Czech Republic

Institute of Molecular and Translational Medicine Faculty of Medicine and Dentistry Palacky University in Olomouc Hnevotinska 3 775 15 Olomouc Czech Republic

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