Oude Meer, The Netherlands (April 2020) – 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, at Kobe University (Professor Chikako Nishigori, lecturer Makoto Kunisada, graduate school student Nozomi Yamano, et al.), have demonstrated a world first via animal experimentation that repeated irradiation of 222 nm ultraviolet radiation (UV-C) with high disinfection capabilities does not cause skin cancer, suggesting that it is safe for exposure to human skin and eyes. This technology is expected to be utilised in a wide range of antibacterial and viral inactivation applications in the medical field, as well as many opportunities for use in 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 28th, at the 2020 American Society of Photobiology Biennial Meeting in Chicago.
This research study was conducted with the support of the KAKENHI 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 222 nm 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 222 nm UV-C is also safe on human skin and eyes.
- The 222 nm UV-C lamp unit used in the research included an optical filter to remove almost all but the required 222 nm wavelength. Irradiation with this lamp unit caused no onset of skin cancer or cataracts*1 to the mice used in the research, which have a high susceptibility to UV radiation.
- The results suggest the direct irradiation of 222 nm germicidal lamps on humans is safe, enabling a wide range of antibacterial and viral inactivation applications in medical fields and daily life.
Background of Research
Naturally occurring UV-C (wavelengths of 200 – 280 nm) is absorbed by the ozone layer and does not reach the Earth’s surface. To make use of the potential for germicidal purposes, lamps emitting 254 nm UV-C have been developed for anti-microbial applications; however, these lamps have only been permitted in locations where people are not present because they present harmful side effects on the human body and may cause skin cancer and cataracts.
The wavelength of the lamp used in this study was 222 nm, which is shorter than 254 nm. 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), 222 nm UV-C is comparable to 254 nm UV-C in terms of the ability to disinfect human skin; but its application in a medical facility required proof of non-carcinogenic exposure to 222nm UV-C, and confirmation of safety regarding direct and repeated exposure to humans.
To investigate the safety of repeated exposure to eyes and skin from 222 nm UV-C germicidal lamps, the researchers repeatedly irradiated a 222 nm germicidal lamp on to 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 222 nm 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 222 nm wavelength.
All mice in the control group which were irradiated with UV-B (wavelengths of 280 – 315 nm) developed skin cancer, and many mice displayed adverse effects of corneal injuries and cataracts. UV-B is the wavelength range within natural sunlight which causes skin cancer.
On the other hand, no mice in the 222 nm germicidal lamp group developed any 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 222 nm irradiation caused no harm was related to the level of skin penetration. Conventional UV radiation reaches the basal layer at the bottom of the skin’s epidermis and damages the cells’ DNA, whereas 222 nm UV-C only reaches the keratinocyte layer at the uppermost superficial layer (the layer which is eventually lost as scurf) and causes no damage to the DNA of epidermic cells.
Development of Ultraviolet Germicidal Irradiation (UVGI) Lamps Safe for Application to Humans
The results of this study indicate that although 222 nm UV-C has a powerful germicidal ability, it can be directly irradiated on human skin. A wide range of antibacterial and viral inactivation applications may be expected in the future, such as hand sanitisation in medical facilities and disinfection in entrance locations at schools, nursing homes, food factories, toilets, and kitchens, etc.
The crystalline lenses in the eyes are mainly made from protein and water. Proteins change and become white and cloudy under a variety of influences, including ageing and years of UV exposure. As a result, the entire lens becomes cloudy, causing impaired vision.
*2 Xeroderma pigmentosum
A genetic disorder in which DNA damage caused by UV radiation cannot be repaired. People with this disorder can develop numerous incidents of skin cancer, from elementary school age and upwards, unless they are protected from UV. In Japan, it affects approximately 5 out of 100,000 people.
Research paper information
- Title: “Long-term effects of 222 nm ultraviolet radiation C sterilizing lamps on mice susceptible to ultraviolet radiation”
- Authors: Nozomi Yamano, Makoto Kunisada, Sachiko Kaidzu, Kazunobu Sugihara, Aiko Nishiaki-Sawada, Hiroyuki Ohashi, Ai Yoshioka, Tatsushi Igarashi, Akihiro Ohira, Masaki Tanito, and Chikako Nishigori
- Journal carrying this article: Photochemistry & Photobiology
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