Far-UVC wavelengths for disinfection are unlikely to harm skin

Far-UVC (200 – 220 nm) has been proposed as an effective disinfection radiation that is safe to humans5. In 2014, Woods et al. undertook a first-in-person study to assess the effect on skin of a 222 nm UVC emitting device … Woods et al. hypothesised that a small amount of longer wavelength UVC radiation above 250 nm (<3%) may be contributing to the observed effects. We wished to determine why these results contrast with other published studies investigating far-UVC sources.

Our results demonstrate that whilst a percentage of far-UVC radiation at 222 nm penetrates to the upper epidermis, there is minimal reaches the mid-epidermis and none in the basal layer. Direct CPD formation in the basal layer observed by Woods et al. is likely to have arisen from very low intensity source emissions above 230 nm, in particular the 270 nm to 310 nm wavelength range, where the spectral emissions are not visualised without plotting incident irradiance on a logarithmic scale. Careful filtering of UVC spectral emissions, to remove unwanted longer wavelengths, has been shown not to induce tissue inflammation or increase pre-mutagenic DNA lesions in both mammalian skin and an in-vitro human skin model 2,5. This supports our conclusion that the longer wavelength ultraviolet radiation was responsible for the effects seen by Woods et al.

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