Kobe University and Ushio Inc. finds evidence of 222nm being non-carcinogenic.
Research conducted by Kobe University and Ushio Inc. examined the potential safety of repeated exposure to 222-nm ultraviolet-C (Far-UVC) light, a wavelength being studied for its ability to inactivate microorganisms while causing less damage to living tissue than conventional germicidal UV. Traditional 254-nm UVC is highly effective against bacteria and other microorganisms, but because it can penetrate more deeply into the skin and eyes, its use has generally been restricted when people are present. The researchers therefore investigated whether 222-nm Far-UVC could offer germicidal benefits with a lower risk of biological damage.
To evaluate the effects of repeated exposure, the researchers used xeroderma pigmentosum group A model mice, which are exceptionally sensitive to ultraviolet radiation and have a substantially greater susceptibility to developing UV-induced skin cancer than normal mice. This provided a stringent model for examining the possible carcinogenic effects of long-term 222-nm Far-UVC exposure. A comparison group was exposed to UVB radiation, the portion of sunlight known to contribute to skin cancer.
The results showed a clear difference between the two types of ultraviolet exposure. The mice exposed to UVB developed skin cancer and experienced additional adverse effects, including cataracts and damage to the cornea. In contrast, the mice repeatedly exposed to the 222-nm Far-UVC source did not develop skin cancer during the study. Microscopic examination of their eyes also found no observable abnormalities associated with the 222-nm exposure.
Researchers attributed this difference largely to the limited penetration depth of 222-nm UVC. Conventional 254-nm germicidal UV can penetrate farther into the skin and reach living cells in deeper layers, where ultraviolet radiation can damage cellular DNA. By comparison, 222-nm Far-UVC was found to penetrate only into the outermost portion of the skin, the stratum corneum, greatly limiting its ability to reach and damage the DNA of living skin cells underneath. This physical characteristic may explain how 222-nm Far-UVC can retain strong germicidal activity while presenting a different biological safety profile from longer-wavelength UV radiation.
Overall, the study provided important early evidence that repeated 222-nm Far-UVC exposure did not produce the carcinogenic skin effects or observable eye damage seen with the comparison UV exposure in this highly UV-sensitive mouse model. The findings supported further investigation of 222-nm technology for germicidal applications in environments where people may be present, including healthcare facilities, schools and other occupied spaces. Because the research was performed in mice, however, the results should be viewed as preclinical safety evidence rather than proof that unrestricted exposure is safe for humans; human use should continue to follow applicable exposure limits and safety standards.
