Terrestrial ultraviolet radiation (UVR) exposure has profound effects on human skin, notably sunburning, photoaging, immunosuppression and photocarcinogenesis. Less attention has been paid to the effects of UVC as we are not naturally exposed to this due to ozone absorption. However, germicidal UVC (254 nm) potently inactivates pathogens and is employed for disinfection purposes but is harmful to human skin and eyes. The development of artificial sources of filtered UVC (Far-UVC; 222 nm) through Krypton Chloride excimer light technology, accelerated during the pandemic given the virucidal effects of Far-UVC and its apparent safety, and commercial roll out of these devices has meant that large scale artificial environmental human Far-UVC exposure is on the horizon in public places. This roll out has exceeded our understanding of the importance of human safety of Far-UVC, and whilst potential major benefits of disinfection using Far-UVC are feasible, we need to balance this with the potential risk to human health, and this is a critical public health issue.
Far-UVC has very limited skin penetration effects, and initial human skin studies indicating safety have been promising. We undertook a two-stage study of the visual and histological effects of Far-UVC in healthy volunteers using single and repetitive exposures to virucidal Krypton Chloride Far-UVC-emitting excimer lamps (PIVUC), using UVB as positive control in a within-subject controlled trial, with visual, reflectance and histological end points, focussing on DNA damage. No significant visual or pathological changes, including cyclobutane pyrimidine dimers and Ki67 staining, were seen (n=20). We have subsequently also seen no visual changes in patients with photosensitivity diseases.
Whilst we need to be cautious in terms of extrapolating these data to larger scale human exposure, this evidence is encouraging with respect to the human safety of Far-UVC, although we must keep an open mind.