Wavelength-dependent DNA photodamage in a 3-D human skin model over the far-UVC and germicidal-UVC wavelength ranges from 215 to 255 nm

The effectiveness of UVC to reduce airborne-mediated disease transmission is well-established. However conventional germicidal UVC (~254 nm) cannot be used directly in occupied spaces because of the potential for damage to the skin and eye. A recently studied alternative with the potential to be used directly in occupied spaces is far-UVC (200 to 235 nm, typically 222 nm), as it cannot penetrate to the key living cells in the epidermis. Optimal far-UVC use is hampered by limited knowledge of the precise wavelength dependence of UVC-induced DNA damage, and thus we have used a monochromatic UVC exposure system to assess wavelength-dependent DNA damage in a realistic 3-D human skin model. We exposed a 3-D human skin model to mono-wavelength UVC exposures of 100 mJ/cm2, at UVC wavelengths from 215 to 255 nm (5-nm steps). At each wavelength we measured yields of DNA-damaged keratinocytes, and their distribution within the layers of the epidermis. No increase in DNA damage was observed in the epidermis at wavelengths from 215 to 235 nm, but at higher wavelengths (240-255 nm) significant levels of DNA damage were observed. These results support use of far-UVC light to safely reduce the risk of airborne disease transmission in occupied locations.