PLOS ONE Published: August 12, 2020

Exploratory clinical trial on the safety and bactericidal effect of 222-nm ultraviolet C irradiation in healthy humans

Tomoaki Fukui ¹,  Takahiro Niikura ¹,  Takahiro Oda ¹, Yohei Kumabe ¹, Hiroyuki Ohashi ²,  Masahiro Sasaki ²,  Tatsushi Igarashi ²,  Makoto Kunisada ³,  Nozomi Yamano ³, Keisuke Oe ¹,  Tomoyuki Matsumoto ¹,  Takehiko Matsushita ¹,  Shinya Hayashi ¹,  Chikako Nishigori ³,  Ryosuke Kuroda ¹ 

¹ Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan. 　
² Ushio Inc., Chiyoda-ku, Tokyo, Japan. 
³ Division of Dermatology, Department of Internal Related, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan. 

 

　従来、殺菌灯として、紫外線のうち主に254nm UV-Cが用いられてきましたが、人体に直接照射すると皮膚の急性傷害の指標である皮膚が赤くなる日焼け反応（紅斑）が現れる事や皮膚がんのリスクもあり、人体への直接照射は難しいとされてきました。しかし、222nm UV-Cの場合、ヒトの皮膚に急性障害が発生しないことが臨床試験で確認されました。具体的には、健常者ボランティア20名を対象として、222 nm UV-C照射の安全性と殺菌性能を検討する事を目的として試験を行い、50-500 mJ/cm²を照射終了後24時間での皮膚紅斑の有無を調べたところ、全ての被験者において、波長 222 nm紫外線照射による紅斑（紫外線による急性障害）を認めませんでした。一方、254 nm UV-C照射による紅斑の最小線量は 10 mJ/cm² と報告されています。また、222nm UV-C照射ヒト皮膚上の菌に対する殺菌効果を確認しました。 



　Conventionally, 254 nm UV-C has been mainly used as a germicidal lamp, however when it is directly irradiated to the human body, it can cause erythema and skin cancer. Whilst, UV radiation with wavelength of 222 nm has been reported that it is much safer than the conventionally used UV radiation with wavelength of 254 nm. According to this report, healthy volunteers were tested with the purpose of examining the safety of UV irradiation with wavelength of 222 nm and its sterilization action on the skin. When the presence or absence of skin erythema (i.e., an acute injury due to UV radiation) was examined 24 h after the end of irradiation, at dose of 50– 500 mJ/cm², no erythema due to UV irradiation with wavelength of 222 nm was observed. On the contrary, the minimum erythema dose due to UV irradiation with wavelength of 254 nm is reported to be 10 mJ/cm². We also confirmed the bactericidal effect against bacteria on human skin with 222nm UV-C. 

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