Origins and Evolution of Photocarcinogenesis Action Spectra, Including Germicidal UVC^†

Abstract

Germicidal ultraviolet radiation (GUV) provides a means of dramatically reducing airborne spread of microorganisms in residential and workspace environments. Regarding design and use of GUV, both efficacy and safety data have accumulated over several decades, with a substantial increase of attention during the current COVID-19 pandemic. Considerations for skin and eye safety previously resulted in guidance on exposures in institutional and workplace settings. This report details the evolution of limits for skin exposures, with particular attention to the risk of skin neoplasia.

Effect of ultraviolet C emitted from KrCl excimer lamp with or without bandpass filter to mouse epidermis

“…To acquire positive control data, a conventional low-pressure Hg lamp named SUV-4 (AS ONE Corporation, Osaka, Japan) was used. This lamp emits principally 254-nm UVC and at least 3~4% of UVB that induces more mutagenic CPD than UVC [ 18 , 19 ]. Irradiance of 254-nm UVC was determined using an S-254/UIT250 (Ushio Inc., Tokyo, Japan).…”

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

“…1), the stratum basale is the deepest layer of the epidermis, where basal cells, including melanocytes, are constantly dividing and migrating upwards; above the stratum basale is the stratum spinosum which contains squamous cells and provides the skin's structural integrity; and above the stratum spinosum is the stratum granulosum which contains dead or dying cells whose nuclei and other organelles are disintegrating as the cells move up into the stratum corneum (37). Thus from a long-term safety perspective, the concern relates to DNA damage to cells in the stratum basale and stratum spinosum, which contain living basal cells, melanocytes and squamous cells (24,25,38). DNA 9 damage to cells in the stratum granulosum or, of course, the stratum corneum is of much less concern, as these contain dead or dying cells.…”

“…1) or to the still deeper stratum basale (basal cell layer, see Fig. 1) of the epidermis, where DNA damage can result in long-term sequelae including carcinogenesis (24,25). Similar considerations apply for the eye with regard to the tear layer and the superficial cells of the cornea.…”

A Need to Revise Human Exposure Limits for Ultraviolet UV‐C Radiation†

“…There were very few if any efforts to measure dermal effects below 254 nm; and UV-C studies were largely limited to 254 nm mutagenic effects on isolated bacteria and human cells in vitro (24,25). Although the cellular studies indicate thresholds for DNA damage, these thresholds require adjustment based upon in vivo preabsorption in living skin (21,22,(24)(25)(26)(27). The limited data led to the initially overly conservative human exposure limits for all wavelengths below 250 nm (2).…”

“…Most in vitro cellular studies of DNA damage, mutagenesis and DNA repair have employed the low-pressure Hg lamp and most concentrated on the emission line at 254 nm, even though UV-C does not exist in terrestrial sunlight (4,5,8,25). Thus, to extrapolate data from laboratory studies of cell cultures and the limited animal studies to human skin (26,27), the actual penetration of UV-C into the basal (germinative) layer of the epidermis (26) had to be applied. Acute damage to the superficial layers of the epidermis would not be TLV ® s for Lasers (dotted lined).…”