Improved Spectral Purity of 222-nm Irradiation Eliminates Detectable Cyclobutylpyrimidine Dimers Formation in Skin Reconstructs even at High and Repetitive Disinfecting Doses

Abstract

UVC222 nm has germicidal effects with potential clinical applications. However, UVC irradiation is capable of inducing DNA damage like cyclobutylpyrimidine dimers (CPD). Although new devices have emission peaks in the short-wavelength region of UVC (~222 nm), the remaining “collateral” radiation at longer wavelengths could be harmful to human health. We investigated the DNA damage caused by far-UVC 222 nm KrCl exciplex radiation on human skin reconstructs after additional filtering using silica filters. The skin reconstructs were irradiated with 100 mJ cm−2, 500 mJ cm−2, and 3 × 500 mJ cm−2 unfiltered and filtered (230–270 nm suppressed) far-UVC or UVB (308 nm) radiation. UVB and non-filtered UVC irradiation induced a significant amount of CPDs, compared with the background. Filtered far-UVC lowered the CPD amount compared with unfiltered UVC and UVB treatments. Repetitive UVC irradiation did not result in the accumulation of CPDs compared with UVB treatment. Reduction in excess of 99.9% of E. coli, S. aureus and C. albicans was detected after applying far-UVC radiation. This identifies a therapeutic window in which microorganisms are killed but tissue is still alive and not damaged, which could give rise to new clinical applications.