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Home » Kobe University-Ushio Inc. Joint Study Shows Irradiation of Filtered 222 nm Far UV-C Light on Human Skin Reduces Bacterial Counts While Causing No Skin Damage

Kobe University-Ushio Inc. Joint Study Shows Irradiation of Filtered 222 nm Far UV-C Light on Human Skin Reduces Bacterial Counts While Causing No Skin Damage

Oude Meer, the Netherlands (August 2020) — Ushio Inc. (TYO: 6925; headquarters in Tokyo, Japan) and a research group led by Dr. Ryosuke Kuroda, Chairman and Professor of the Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, have completed a research study that shows that irradiation of filtered 222 nm UV-C light on human skin reduces bacterial counts while causing no injury to the skin. This is the first study on the safety of 222 nm far UV-C light conducted on humans. The research paper regarding this study is published on PLOS ONE and can be accessed here.

In this study, Ushio’s Care222® UV-C disinfection* device irradiated 500 mJ/cm2 of 222 nm UV-C light on the back of 20 healthy volunteers aged from 20 to 80 years. The Care222 device includes an optical filter that eliminates radiation from wavelengths above 230 nm. Twenty-four hours after the irradiation, none of the participants showed any signs of erythema (redness of skin).

The back of each participant was irradiated again with 500 mJ/cm2 of 222 nm UV-C light using the Care222 device to measure the bacterial flora count on the skin scraped with a swab. The bacterial flora count was taken pre-irradiation, 5 minutes after irradiation, and 30 minutes after irradiation. The bacterial flora count significantly decreased—by almost 90%—after irradiation with the Care222 device.

When the irradiated area of the participants was assessed three months post-irradiation, none of them showed any signs of erythema, and no adverse event was noted.

Based on these findings, the researchers concluded that irradiation of filtered 222 nm UV-C is safe and has a bactericidal effect on the human skin. Note that a previous joint study between Kobe University and Ushio Inc. showed that repeated irradiation of filtered 222 nm UV-C light did not cause skin cancer or cataract to hairless mice (a type of mice with extra sensitive skin). Our press release about this research study can be accessed here.

It is important to use filtered 222 nm UV-C light in occupied spaces. Unfiltered 222 nm UV-C lamps will emit radiation in the 230 nm (UV-C) to 320 nm (UV-B) range. Irradiation without blocking these higher wavelengths of light has been reported to cause erythema at 50 mJ/cm2 and damage to the cellular DNA at 63 mJ/cm2 or more.

Kobe Uni. and Ushio Inc found no evidence of skin damage after reducing bacteria present on humans with 222nm far UV-C irradiation

Ushio’s Care222 device features a patented short band-pass filter that prevents harmful, longer UV wavelengths beyond 230 nm from being emitted by the lamp.

Ushio's Care222 U3 module | Ushio Europe B.V.

For more information about the properties of 222 nm UV light and Care222 excimer lamps, please visit

*Any references to “disinfection” are referring generally to the reduction of pathogenic bioburden and are not intended to refer to any specific definition of the term as may be used for other purposes by the U.S. Food and Drug Administration, the U.S. Environmental Protection Agency, or any other international governing body.

The Care222 standard character mark and stylized logo mark are registered trademarks of Ushio America, Inc., in the United States, European Union, and United Kingdom.

About Ushio Europe B.V.

Ushio Europe does not simply sell lighting products, but instead seeks to understand your specific needs and present you with unique solutions. Ushio has amassed a wealth of in-house specialist knowledge and localised expertise, with dedicated facilities designed and implemented for the testing of ultraviolet, visible, and infrared light solutions. From the early stages of research and development to the final implementation, Ushio Europe commits to the technical development of your process solution until you are 100% satisfied with the outcome. The Ushio aftercare team is legendary thanks to its understanding that needs change along with the processes that solve them. With that in mind, Ushio’s experts are always available for your questions and any additional modifications that come up further down the line. Ushio uniquely tailors each individual project to the client and presents results which reach far beyond expectation. Ushio does not merely wish to meet your requirements; it vows to surpass them entirely.

Further Reading with Ushio Europe

Care222 product page
Ushio Care222® Far UV-C Disinfection Modules (detailed specifications)
Excimer: The Technology Explained – An Ushio Europe learning resource

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