Mouse Skin Reactions to 222nm and 235nm UV-C Light Exposure

Biological response and DNA damage following irradiation with shorter wavelengths in the UV-C range were evaluated to investigate the safety at three wavelengths because of the recent emergence of germicidal equipment emitting short-wavelength UV-C for various purposes, including medical uses. To estimate an acceptable safety dose for human skin in the UV-C range, especially short UV-C, we studied the biological effects of 207 nm, 222 nm, and 235 nm UV-C using albino hairless mice and evaluated the inflammatory reactions in the skin. To explore an appropriate indicator to evaluate the biological response, we employed determination of the minimal perceptible response dose (MPRD), by which any subtle cutaneous response; erythema, edema, and scale could be observed by visual inspection. Erythema was rarely observed, but edema and scale formation were evident for short UV-C wavelengths. The MPRD at 207, 222, and 235 nm was determined to be > 15 kJ/m2, 15 kJ/m2, and 2.0 kJ/m2, respectively. These values could be thresholds and indicators for possible safety assessments. Our data suggest that the current human exposure limits for short UV-C wavelengths below 254 nm are overly restrictive and should be reconsidered for future disinfection lamps with short UV-C wavelengths.

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