Knowledge UV Disinfection: Repetitive Irradiation with 222nm UV-C Does Not Cause Skin Cancer


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Ushio Inc. (TYO: 6925; headquarters in Tokyo, Japan) and a research group from the Division of Dermatology, Department of Internal Medicine, Graduate School of Medicine, Kobe University (Professor Chikako Nishigori, lecturer Makoto Kunisada, graduate school student Nozomi Yamano, et al.), demonstrated for the first time in the world via animal experimentation that repeated irradiation of 222nm ultraviolet radiation (UV-C) with high disinfection power does not cause skin cancer, suggesting its safety on human skin and eyes. This technology is expected to be utilized in a wide range of antibacterial and viral inactivation applications in the medical field and daily life.

The results of this research were published online in Photochemistry & Photobiology on March 29, 2020, and will be presented by Professor Nishigori on June 28 during the 2020 American Society of Photobiology Biennial Meeting in Chicago.

This research study was conducted with the support of the Grants-in-Aid for Scientific Research provided by the Ministry of Education, Culture, Sports, Science and Technology (JP16k10126).


  • The research study demonstrated for the first time in the world that repeated irradiation of 222nm ultraviolet radiation (UV-C) does not cause skin cancer when it was applied to mice with extra susceptible skin.
  • The results of the research suggest that repeated irradiation of 222nm UV-C is also safe on human skin and eyes.
  • The 222nm UV-C lamp unit used in the research included an optical filter to remove nearly all but the dominant 222nm wavelength. Irradiation with this lamp unit caused no onset of skin cancer or cataracts*1 to the mice used in the research that are very susceptible to UV.
  • These results suggest direct irradiation of 222nm germicidal lamps on humans is safe, enabling a wide range of antibacterial and viral inactivation applications is expected in the medical field and daily life.

Background of Research

UV-C (wavelength of 280-200nm) is absorbed in the ozone layer and does not reach the Earth’s surface. To exploit its strong germicidal power, germicidal lamps emitting 254nm UV-C have been developed and used for anti-microbial applications. But these lamps have only been used in locations where people are not present because they have harmful side effects on the human body and may cause skin cancer and cataracts.

The wavelength of the lamp used in this study was 222nm, which is shorter than 254nm. Its development started in the hope that it can be used in the medical field. According to the Division of Orthopedic Surgery at Kobe University (Professor Ryosuke Kuroda), 222nm UV-C is comparable to 254nm UV-C in terms of the ability to sterilize human skin. But its application in a medical facility has required proof that repeated exposure to 222nm UV-C is non-carcinogenic and safe because of the possibility that it could be directly and repeatedly irradiated on humans.

Research Methodology

To investigate the safety of repeated exposure of eyes and skin to 222nm UV-C germicidal lamps, the researchers repeatedly irradiated a 222nm germicidal lamp onto xeroderma pigmentosum group A*2 model mice. This type of mouse is known to have an approximately 10,000-fold increased risk of developing skin cancer compared to wild-type mice. The 222nm lamp unit used in the study included a krypton-chloride (Kr-Cl) excimer lamp and an optical bandpass filter to remove nearly all but the dominant 222nm wavelength.

All mice in the control group onto which UV-B (wavelength of 280-315nm) was irradiated developed skin cancer, and many mice displayed adverse effects of corneal injuries and cataracts. UV-B is the wavelength range of the sunlight that causes skin cancer.

On the other hand, no mice in the 222nm germicidal lamp group developed skin cancer, nor were any abnormalities found at the microscopic level upon an analysis conducted with the support of the Division of Ophthalmology at Shimane University (Professor Masaki Tanito) (Fig. 1).

In addition, it became clear that the reason 222nm irradiation caused no harm was related to the level of skin penetration. The conventional UV radiation reaches the basal layer at the bottom of the skin’s epidermis and damages the cells’ DNA, whereas 222nm UV-C only reaches the keratinocyte layer at the uppermost superficial layer (the layer that becomes scurf) and causes no damage to the DNA of epidermic cells.

About Ushio Care222®

The Care222® series is Ushio's new line of 222nm Far UV-C excimer lamps for microbial reduction.

Care222 is presently used for unoccupied spaces with ongoing studies to make Care222 your future choice for all occupied and unoccupied microbial reduction solutions. Features of the Care222 lamp allow customers to obtain 100% light output in less than a second, whereas the conventional germicidal lamp starts at only 50% output and takes several minutes to achieve 100% output.

These mercury-free and instant-start excimer lamps (available in 12W module, 20W and 300W lamp) are ideal for bathrooms, toilets, counter tops, and other occasional-use applications.

For more information about Ushio's Care222® Products: please visit

About Ushio America, Inc.

Ushio America, Inc. is a vertically integrated solutions company for lighting systems and components utilizing xenon short arc, lasers, ultra-high-pressure UV, excimer, metal halide, LEDs (specialty sensing and architectural lighting), halogen, fluorescent, and miniature incandescent lamps serving semiconductor, printed circuit, video projection, cinema, medical, life sciences, UV curing, germicidal, horticulture, landscaping, graphic arts, flashlight, scientific, medical, infra-red heating, lamp and laser drivers, systems and services, and numerous other applications. Established in 1967 as a subsidiary of Ushio Inc., in Tokyo, Japan, Ushio America offers a full spectrum of over 2,500 products and services to its customers.
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