FAR UVC LIGHT SKIN
The effect of irradiation on skin redness was determined by calculating Δa the difference in a* at a given time point, a*(t), compared with preirradiation, a*(0). The reflectance spectrophotometer output provides three values which represent L* (lightness from black to white), a* (from green to red) and b* (from blue to yellow) from the 1976 CIELAB color space. All exposure areas were covered between time point assessments. On yet another exposure (2000 s), a second set of filtering was introduced to the far-UVC source to further reduce the low-power long-wavelength emissions. With one exposure (2000 s), the skin was tape stripped 1 h after exposure. Exposure sites were assessed visually and with a reflectance spectrophotometer (CM-700d with 8 mm aperture, Konica Minolta Inc., Tokyo, Japan) at hourly intervals from zero up to twelve hours and at 24 h. 5 × 5 cm areas on the left and right inner forearms were exposed on several occasions for exposure times of 250, 1000, 20 s. MATERIALS AND METHODS In-vivo exposureĪ 37-year-old male, Fitzpatrick Skin Type II, performed multiple self-exposures with a filtered KrCl excimer far-UVC system with a peak wavelength emission at 222 nm (SafeZoneUVC, Ushio Inc., Tokyo, Japan).
This proof-of-concept testing could then inform future detailed and controlled assessment. The authors of this study hypothesized that it may be longer wavelengths present in the lamp spectrum that caused the adverse effects, a hypothesis supported by subsequent computer modeling ( 15).ĭue to the unsupported but widely disseminated commercial claims of far-UVC systems being “safe for humans,” it was felt that there was a need for rapid proof-of-concept testing on human skin with an appropriately filtered far-UVC device.
At the beginning of the COVID-19 pandemic, the only published study investigating a far-UVC system in humans had contradicted the laboratory results, showing skin damage in the form of erythema and cyclobutane pyrimidine dimer (CPD) formation ( 14). These laboratory data are being used commercially to intensively promote and sell far-UVC systems to the global public. However, it does not induce premutagenic DNA lesions in mouse skin, even when chronically irradiating mice particularly susceptible to ultraviolet radiation ( 11- 13). It has been demonstrated that far-UVC, emitted by KrCl excimer lamps, inactivates SARS-CoV-2 on surfaces as well as human coronaviruses alpha HCoV-229E and beta HCoV-OC43 in air ( 9, 10). Current far-UVC published research is dominated by Krypton-Chloride (KrCl) excimer lamps, which emit predominantly at 222 nm but can include low-power long-wavelength emissions. The established UVC wavelength routinely used for germicidal tasks is the mercury emission wavelength of 253.7 nm, which has been shown to inactivate SARS-CoV-2 but also results in acute adverse reactions in the skin and eyes ( 7, 8).įar-UVC is a term, which loosely incorporates wavelengths between 200 and 230 nm. UVC irradiation is a well-established technology used for the destruction of bacteria and viruses and employed in a range of industries ( 3- 6). Ultraviolet-C (UVC) radiation covers the wavelength range of 100–280 nm and has a known germicidal effect ( 2). As a consequence, it is imperative to employ measures that inactivate or destroy the virus and limit its transmission. As of May 2020, the pandemic had also resulted in an estimated 3.8 trillion dollars of global consumption losses and 147 million job losses ( 1). Estimates as of the 4 th of December 2020 indicate 65.6 million confirmed coronavirus cases and approximately 1.5 million deaths globally ( ). The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus responsible for the current global COVID-19 pandemic. This work also contributes to growing arguments for the exploration of exposure limit expansion, which would subsequently enable faster inactivation of viruses. These results combined with Monte Carlo Radiative Transfer computer modeling suggest that filtering longer ultraviolet wavelengths is critical for the human skin safety of far-UVC devices. No erythema was observed at any time point with exposures up to 18 000 mJ cm −2. No visible skin changes were observed at 1500 mJ cm −2 whereas, skin yellowing that appeared immediately and resolved within 24 h occurred with a 6000 mJ cm −2 exposure. A Fitzpatrick Skin Type II individual exposed their inner forearms to large radiant exposures from a filtered Krypton-Chloride (KrCl) far-UVC system (SafeZoneUVC, Ushio Inc., Tokyo, Japan) with peak emission at 222 nm. We felt there was a need for rapid proof-of-concept human self-exposure, to inform future controlled research and promote informed discussion. Far-UVC devices are being commercially sold as “safe for humans” for the inactivation of SARS-CoV-2, without supporting human safety data.
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