Indoor UVC light can put us back on the road to normality

Dr. David Brenner, Columbia University


After two years of Covid we still struggle to find that path back to normal indoor life. We can’t keep vaccinating every six months, and we certainly won’t wear masks indefinitely.  We do know that if we markedly increase indoor ventilation, person-to-person transmission of viruses will decrease, but that’s simply not practical in most situations. We really need new ways to bring our indoor life back to normal.

A proven way forward is ultraviolet (UV) light. We’re all familiar with UVA and UVB light, which are part of normal sunlight and give us our suntans and our sunburns. But there is a third type of UV light, UVC, which is not part of the earth’s sunlight, but can be made with UVC lamps.

It’s been known for decades that UVC is super efficient at killing all types of viruses in the air, so it’s a superb choice for disinfecting indoor air. By simply adding UVC lights to conventional indoor overhead lighting, we can quickly kill essentially all the viruses floating in the air, and so protect ourselves against indoor person-to-person disease transmission.

But of course, for this approach to be useful we have to be completely sure that the UVC light that we use is completely safe for direct human exposure.  And “conventional” UVC light, all that was available till recently, does potentially pose a small risk to the skin and eyes if it is shined directly near people in an occupied room. But here’s the new twist: scientists have now identified and developed a new safe type of UVC light – called far-UVC light – which is both safe for use in the air around people and also highly effective at killing airborne viruses.


How do we know that far-UVC is safe? It’s safe because the outer surface of our skin contains a protective layer of dead cells, and the surface of our eyes is covered by a protective tear layer; far -UVC light, uniquely, simply can’t penetrate through these protective layers to reach the living cells in our skin and eyes. Following from this basic idea, over the past few years multiple research labs worldwide have performed and published far-UVC safety studies for skin and eye, human ( e.g., Welch et al 2022a, Eadie et al 2021) and mice (e.g., Welch et al 2022). The bottom line is that when far-UVC lamps are used with regulatory limits, there is no evidence at all of any adverse health effects. To back this up, following from all of these studies the US agency that sets the safety regulations for UV light has just (January 2022) upped the recommended far-UVC exposure limit to well above what will actually be used in practice.

Fig 1 (from Welch et al 2022a ). Amount  of DNA damage in human skin produced by the same exposure to conventional UVC vs far-UVC. Unlike conventional UVC, far-UVC did not produce DNA damage in human skin

How do we know that far-UVC works? Laboratory studies first showed that far-UVC is super efficient at killing airborne viruses, including coronaviruses and flu viruses – the type of virus or variant simply doesn’t matter. And scaling up to full-sized rooms, the most recent studies, by a joint UK-US team, have now been done in a full-sized room continuously filled with airborne microbes – just like a room with people who are continuously coughing: their results (Eadie et al 2022) imply that safe levels of far-UVC light in an occupied room can provide almost as much protection as simply stepping outside into the open air.

Fig 2 (from Eadie et al 2022). Very rapid reduction in the amount of airborne microbes in a full-sized room containing a continuous source of airborne microbes and realistic ventilation.

The red curve shows a rapid 92% reduction when far-UVC lights were used within 2021 safety limits.
The blue curve shows an even more rapid 98% reduction when the far-UVC lights were used within the new (2022) safety limits.

The deployment of Krypton Far UV Lighting at the Centers of Excellence for Influenza Research and Response was made possible by the generosity of Far UV Technologies, Inc of Kansas City, MO. 

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Peer-Reviewed Published Papers on Safety and Efficacy of filtered Far UVC Light

(Updated as of April 2022)

 A. Safety of far-UVC Light

  1. Buonanno M, Randers-Pehrson G, Bigelow AW, Trivedi S, Lowy FD, Spotnitz HM, Hammer SM, Brenner DJ. 207-nm UV light – a promising tool for safe low-cost reduction of surgical site infections. I: in vitro studies. PLoS One 2013;8:e76968.
  2. Buonanno M, Ponnaiya B, Welch D, Stanislauskas M, Randers-Pehrson G, Smilenov L, Lowy FD, Owens DM, Brenner DJ. Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light. Radiat Res 2017;187:483-91.
  3. Buonanno M, Stanislauskas M, Ponnaiya B, Bigelow AW, Randers-Pehrson G, Xu Y, Shuryak I, Smilenov L, Owens DM, Brenner DJ. 207-nm UV Light-A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. II: In-Vivo Safety Studies. PLoS One 2016;11:e0138418.
  4. Kaidzu S, Sugihara K, Sasaki M, Nishiaki A, Igarashi T, Tanito M. Evaluation of acute corneal damage induced by 222-nm and 254-nm ultraviolet light in Sprague-Dawley rats. Free Radic Res 2019;53:611-7.
  5. Fukui T, Niikura T, Oda T, Kumabe Y, Ohashi H, Sasaki M, Igarashi T, Kunisada M, Yamano N, Oe K, Matsumoto T, Matsushita T, Hayashi S, Nishigori C, Kuroda R. Exploratory clinical trial on the safety and bactericidal effect of 222-nm ultraviolet C irradiation in healthy humans. PLoS One 2020;15:e0235948.
  6. Cadet J. Harmless Effects of Sterilizing 222-nm far-UV Radiation on Mouse Skin and Eye Tissues. Photochem Photobiol 2020;96:949-50.
  7. Barnard IRM, Eadie E, Wood K. Further evidence that far-UVC for disinfection is unlikely to cause erythema or pre-mutagenic DNA lesions in skin. Photodermatol Photoimmunol Photomed 2020;36:476-7.
  8. Hanamura N, Ohashi H, Morimoto Y, Igarashi T, Tabata Y. Viability evaluation of layered cell sheets after ultraviolet light irradiation of 222 nm. Regen Ther 2020;14:344-51.
  9. Yamano N, Kunisada M, Kaidzu S, Sugihara K, Nishiaki-Sawada A, Ohashi H, Yoshioka A, Igarashi T, Ohira A, Tanito M, Nishigori C. Long-term Effects of 222-nm ultraviolet radiation C Sterilizing Lamps on Mice Susceptible to Ultraviolet Radiation. Photochem Photobiol 2020;96:853-62.
  10. Hickerson RP, Conneely MJ, Tsutsumi SKH, Wood K, Jackson DN, Ibbotson SH, Eadie E. Minimal, superficial DNA damage in human skin from filtered far-ultraviolet-C (UV-C). Br J Dermatol (2021) https://doiorg/101111/bjd19816.
  11. Buonnano M, Welch D, Brenner DJ. Exposure of human skin models to KrCl excimer lamps: The impact of optical filtering.  Photochemistry and Photobiology (2021);97:517-23
  12. Kaidzu S, Sugihara K, Sasaki M, Nishiaki A, Ohashi H, Igarashi T, Tanito M. Re-Evaluation of Rat Corneal Damage by Short-Wavelength UV Revealed Extremely Less Hazardous Property of Far-UV-C. Photochem Photobiol 2021;97:505-16.
  13. Eadie E, Barnard IMR, Ibbotson SH, Wood K. Extreme Exposure to Filtered Far-UVC: A Case Study. Photochem Photobiol 2021;97:527-31.
  14. Eadie E, O’Mahoney P, Finlayson L, Barnard IRM, Ibbotson SH, Wood K. Computer Modeling Indicates Dramatically Less DNA Damage from Far-UVC Krypton Chloride Lamps (222 nm) than from Sunlight Exposure. Photochem Photobiol 2021;97:1150-1154
  15. Welch D, Aquino de Muro M, Buonanno M, Brenner DJ. Wavelength-dependent DNA photodamage in a 3-D human skin model over the far-UVC and germicidal-UVC wavelength ranges from 215 to 255 nm. Wavelength-dependent DNA Photodamage in a 3-D human Skin Model over the Far-UVC and Germicidal UVC Wavelength Ranges from 215 to 255 nm. Photochem Photobiol. 2022 Feb 1. doi: 10.1111/php.13602
  16. David Welch, Norman J. Kleiman, Peter C. Arden, Christine L. Kuryla, Manuela Buonanno, Brian Ponnaiya, Xuefeng Wu, David J. Brenner. No evidence of induced skin cancer or other skin abnormalities after long term (66 week) chronic exposure to 222-nm far-UVC radiation.

B. Anti-Microbial Efficacy of Far-UVC Light

  1. Buonanno M, Ponnaiya B, Welch D, Stanislauskas M, Randers-Pehrson G, Smilenov L, Lowy FD, Owens DM, Brenner DJ. Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light. Radiat Res 2017;187:483-91.
  2. Buonanno M, Welch D, Shuryak I, Brenner DJ. Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses. Sci Rep 2020;10:10285.
  3. Welch D, Buonanno M, Grilj V, Shuryak I, Crickmore C, Bigelow AW, Randers-Pehrson G, Johnson GW, Brenner DJ. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep 2018;8:2752.
  4. Jung WK, Park KT, Lyoo K-S, Park S-J, Park YH. Demonstration of antiviral activity of far-UVC microplasma lamp irradiation against SARS-CoV-2. Clin Lab 2021;67:1955-8.
  5. Kitagawa H, Nomura T, Nazmul T, Kawano R, Omori K, Shigemoto N, Sakaguchi T, Ohge H. Effect of intermittent irradiation and fluence-response of 222 nm ultraviolet light on SARS-CoV-2 contamination. Photodiagnosis Photodyn Ther 2021;33:102184.
  6. Kitagawa H, Nomura T, Nazmul T, Omori K, Shigemoto N, Sakaguchi T, Ohge H. Effectiveness of 222-nm ultraviolet light on disinfecting SARS-CoV-2 surface contamination. Am J Infect Control 2021;49:299-301.
  7. Kitagawa H, Kaiki Y, Tadera K, Nomura T, Omori K, Shigemoto N, Takahashi S, Ohge H. Pilot study on the decontamination efficacy of an installed 222-nm ultraviolet disinfection device (Care222), with a motion sensor, in a shared bathroom. Photodiagnosis Photodyn Ther 2021;34:102334.
  8. Janisiewicz W, Takeda F, Evans B, Camp M. Potential of far ultraviolet (UV) 222 nm light for management of strawberry fungal pathogens. Crop Protection 2021;150:105791
  9. Goh JC, Fisher D, Hing ECH, Hanjing L, Lin YY, Lim J, Chen OW, Chye LT. Disinfection capabilities of a 222 nm wavelength ultraviolet lighting device: a pilot study. J Wound Care 2021;30:96-104.
  10. Glaab J, Lobo-Ploch N, Cho HK, Filler T, Gundlach H, Guttmann M, Hagedorn S, Lohan SB, Mehnke F, Schleusener J, Sicher C, Sulmoni L, Wernicke T, Wittenbecher L, Woggon U, Zwicker P, Kramer A, Meinke MC, Kneissl M, Weyers M, Winterwerber U, Einfeldt S. Skin tolerant inactivation of multiresistant pathogens using far-UVC LEDs. Sci Rep 2021;11:14647.
  11. Buchan AG, Yang L, Atkinson KD. Predicting airborne coronavirus inactivation by far-UVC in populated rooms using a high-fidelity coupled radiation-CFD model. Sci Rep 2020;10:19659.
  12. Buchan AG, Yang L, Welch D, Brenner DJ, Atkinson KD. Improved estimates of 222 nm far-UVC susceptibility for aerosolized human coronavirus via a validated high-fidelity coupled radiation-CFD code. Sci Rep. 2021;11(1):19930
  13. Ewan Eadie, Waseem Hiwar, Louise Fletcher, Emma Tidswell, Paul O’Mahoney, Manuela Buonanno, David Welch, Catherine S. Adamson, David J. Brenner, Catherine Noakes, Kenneth Wood. Far-UVC efficiently inactivates an airborne pathogen in a room-sized chamber. Nature Scientific Reports 2022 Mar 23;12(1):4373.