Does UV Kill the Coronavirus? Here’s What We Know
Roopinder Tara posted on May 05, 2020 |
Slow and safe with UV-A or fast and dangerous with UV-C
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SARS-CoV-2, the coronavirus causing the COVID-19 disease, can indeed be destroyed by ultraviolet light, or UV, as has been recently suggested. But it is not as simple as just going out in the sun or passing your hands under a blacklight.

You’d have to wait seven days for the sun to do its work on a used mask, for example, according to Jim Malley, an environmental engineer at the University of New Hampshire.

By that time, the virus has already self-destructed. The SARS-CoV-2 cannot tolerate conditions outside of bodies and withers quickly. In a lab experiment, it lasted three days on plastic, two days on stainless steel and one day on cardboard[i].

We may reasonably assume direct sunlight would accelerate its destruction. SARS-CoV, the predecessor of our current coronavirus pandemic, suffered under sunlight. A 2013 study calculated that it would take 1.3 to two hours under the midday sun in Washington, D.C., or New York City during the summer solstice to incapacitate most of the coronaviruses on a glove—though viruses in the largest globules unscathed.

The shorter the wavelength of UV, the more effective it is against viruses. Sunlight, mostly in the UV-A range, cannot compare to UV-C, which has proven so successful against all germs that it is referred to as germicidal UV. Germicidal UV has been adopted to sanitize hospital surfaces and medical instruments. According to a 2005 study, it works particularly well against coronaviruses.

So, why can’t it help humans fight off the COVID-19? For one thing, the atmosphere blocks 100 percent of UV-C radiation from the sun so none of it will incapacitate the SARS-CoV-2 in the air, on your skin or other surfaces. UV-C also has to be generated by special lamps.

The use of UV-C directly on or in humans is problematic.

Turning industrial UV on ourselves “would literally be frying people,” said Dan Arnold, sales and marketing manager for UV Light Technology in Birmingham, UK, in a BBC article. UV-C not only destroys viruses by scrambling their genomes, but it is also extremely dangerous to all living cells. Arnold has had to dissuade supermarket managers from installing his company’s equipment at the entrance of their stores.

The ABCs of UV

In the spectrum of electromagnetic radiation from the sun, the UV band occupies the 400nm to 10nm range. (Image courtesy of ESA / AOES Medialab.)
In the spectrum of electromagnetic radiation from the sun, the UV band occupies the 400nm to 10nm range. (Image courtesy of ESA / AOES Medialab.)

UV in the electromagnetic radiation spectrum between visible light and X-rays is further split up as UV-A, UV-B and UV-C.

UV was discovered in 1801 by German physicist Johann Wilhelm Ritter.

UV ranges are defined by the US Navy as follows:

UV-A, 315-400nm wavelength, is the least harmful. At the edge of the visible spectrum, its bluish light is popularly referred to as black light. You’ve seen bodily fluids fluoresce under UV-A in crime scenes – hopefully only in TV and movies.  Insects and birds can see UV-A. Hawks will track the UV off urine trails right up to a rodent. The lens in the human eye blocks UV from the retina except in the rare case of aphakia, a condition where the lens is missing or removed. After impressionist Claude Monet had his lenses removed with cataract surgery, his scenes became increasingly bluish. Aphakic observers were recruited by the U.S. military during WWII to detect UV signals from offshore German U-boats[ii].

UV-B, 280-315nm wavelength, is more likely to damage cells, acting on the melanin of skin, as well as the cells’ genetic material. DNA is affected the most, but so is RNA, the genetic material in coronaviruses. 95 percent of UV-B is blocked by the ozone layer.

UV-C, 180-280nm wavelength, is known and accepted as germicidal, though, technically, it may not incapacitate the organism as much as destroy its genetic material and, therefore, its ability to replicate. UV-C’s destruction of genetic material is indiscriminate. It doesn’t care if the cells are in plants, animals, yeasts, bacteria, viruses or humans. Our atmosphere blocks all of the sun’s UV-C from the Earth’s surface.

Extreme UV, 10-180nm, is sometimes called vacuum UV for its inability to propagate unless in a vacuum.

A bus undergoes UV-C treatment in Shanghai, China. Using 210 tubes emitting UV-C radiation, both inside and outside the bus,  Yanggao claims to have brought a 40-minute sterilization process down to five minutes, allowing the disinfection of 250 buses a day. (Image courtesy of YouTube.)
A bus undergoes UV-C treatment in Shanghai, China. Using 210 tubes emitting UV-C radiation, both inside and outside the bus, Yanggao claims to have brought a 40-minute sterilization process down to five minutes, allowing the disinfection of 250 buses a day. (Image courtesy of YouTube.)

How Does UV Kill Viruses?
Technically, viruses cannot be “killed” because they are not alive in the biological sense of the word. However, they can be made unable to replicate using UV radiation. The UV radiation, UV-C in particular, is absorbed by DNA and RNA, altering its structure. The virus may still be moving, looking for a host cell, but its genetic material is compromised. It cannot replicate. Game over.

As the frequency of radiation increases, getting further from the visible spectrum until it reaches the next classification of radiation (X-rays), it gets more lethal. 

E = h · ƒ

Where E= energy in Joules, or J

And h = 6.626 × 10-34 J·s, or Planck's constant

While the effect of UV on the body at the atomic level is not known or observable, it is theorized that as the frequency of light increases, it causes resonances in different sizes of cell structures, molecules and atoms—all the way to subatomic particles. With particles energized enough, they break free of the bonds that hold them together.  X-rays and gamma rays are called ionizing radiation for their ability to break off positive ions (alpha decay, a proton and a neutron) or negative ions (electrons and neutrons).

“UV-C radiation is sufficiently energetic that individual photons may produce chemical bond breakage and ionization of some atoms and molecules,” said George Chabot, Ph.D., professor emeritus at UMass Lowell, in a public health forum. “The preferential absorption of particular energy photons by materials, both organic and inorganic, is evident throughout the electromagnetic spectrum from microwaves through infrared and visible light, ultraviolet, X-rays and gamma rays.”

The frequencies of UV are particularly damaging to DNA and RNA. The SARS-CoV-2 virus has coils of RNA in its nucleus, which it injects into a host cell to take over the cell, causing a chain reaction that results in an infection.

UV-C is absorbed by the RNA in a coronavirus and makes molecules in the RNA rearrange themselves into dimers (from “di” meaning two, and “mer” from parts), resulting in RNA that will not pair and,  therefore, will not allow the virus to replicate. UV-B radiation will also make dimers, but it is 20 to 100 times less effective than UV-C, according to a 2004 study on Inactivation of the Coronavirus. UV-A is too weakly absorbed by DNA and RNA and far less effective in making dimers.

Can UV Be Used as a Treatment for COVID-19 Patients?

The idea of treating COVID-19 with UV may have come from UV-A light treatments used for skin conditions, including eczema, psoriasis, vitiligo and T-cell lymphoma, a type of skin cancer. UV light treatments go back to the early 20th century. Danish physician Niels Ryberg Finsen won a Nobel Prize in 1903 for a light therapy used to fight skin tuberculosis.

There have been reports of researchers suggesting far UV-C (wavelength range of 220 to 225), may be less damaging to human tissues, but those studies are still on mice. The effect on humans is not known, so Malley is part of the consensus of medical experts who do not recommend it as a treatment for COVID-19.

With the public tantalized by a surefire virus killer, the International Ultraviolet Association (IUVA) felt compelled to issue this warning:

“We would like to inform the public that there are no protocols to advise or to permit the safe use of UV light directly on the human body at the wavelengths and exposures proven to efficiently kill viruses such as SARS-CoV-2. UV light under the conditions known to kill such viruses are also known to cause severe skin burns, skin cancer, and eye damage. We strongly recommend that anyone using UV light to disinfect medical equipment, surfaces, or air in the context of COVID-19, applications that are supported by sound scientific evidence, follow all recommended health and safety precautions and to avoid direct exposure of the body to the UV light.”

What About Industrial and Medical Use of UV-C?

A range of UV-C radiation, between 254 and 270nm, has found application as a germicide, usable against all manner of viruses, like H5N1, swine flu and SARS plus “superbugs,” as the class of drug-resistant bacteria, viruses and fungi, such as CRE, C. diff, MRSA, have come to be known.

“UV light, more specifically germicidal UV or far UV-C, can be very effective at inactivating viruses, bacteria and other human pathogens and if properly designed and operated can be a successful application for disinfecting PPEs, surgical instruments, air and water,” said Jim Malley, professor of civil and environmental engineering at the University of New Hampshire, in a statement released to the press.

UV-C has been used to disinfect water, air systems and surfaces for over a hundred years, and its effectiveness is supported by decades of scientific research, according to the IUVA. Whereas the UV exposure required to inactivate different microorganisms varies, there are no known microorganisms that can survive it. It is regularly and often to purify air, water and surfaces against bacteria, viruses, fungi and protozoa. 

Denmark’s UVD Robots claims to eliminate 99.99 percent of all viruses from room air and surfaces and has been purchased by hospitals in China.  It included built-in safeguards to make sure no patients are in the room.

However, UV-C cannot disinfect where it cannot “see,” so its disinfection is limited to direct and reflected rays. Germs in cracks, the weave of fabrics, the folds of bed sheets, behind furniture, under rugs, etc., will be unaffected. Therefore, complete sterilization must have, in addition to UV-C, a wipe-down with a disinfecting solution or washing with soap or detergent.

Why Is UV So Hard on Skin and Eyes?

UV-A and UV-B radiation on the skin cause sunburn. UV-C radiation, which is much more energetic, would cause a worse, quicker sunburn. Luckily, 100 percent of it is blocked by the atmosphere. A suntan is melanin that gathers on the skin as a reaction to UV-A and UV-B. Melanin absorbs the radiation and dissipates as heat. The darker the skin is, the more melanin present. However, the darkest of skin only has an SPF (sun protection factor) of 13.4[iii], so sunscreen is still advisable.

Continued exposure increases the risk of skin cancer, including melanoma that occurs when melanin cells (melanocytes) grow out of control, and other skin conditions.

“We’re talking about light waves at low wavelengths that contain a lot of energy, and that energy has been shown in many studies to be extremely damaging to human tissues, in particular, the skin and the eyes,” said Professor Malley.

Eyes are particularly sensitive to UV radiation. Sunglasses should be worn to protect eyes from UV exposure. Snow blindness, the common name for photokeratitis, is caused by reflected UV-A and UV-B rays from snow, water or sand.

In manufacturing, photokeratitis results from looking directly at the light from a welding operation and goes by the names of arc-eye or welders flash.

Photokeratitis can be temporary blindness, but repeated exposure can lead to cataracts and permanent blindness.

Though limits of UV-C is regulated, the IUVA recommends we totally avoid UV-C exposure.

Could Ordinary Sunlight Prevent the Spread of the COVID-19 Virus?

 (Image courtesy of WHO.)
(Image courtesy of WHO.)

Sunlight definitely will not prevent COVID-19 spread, said the World Health Organization (WHO) in no uncertain terms. “Exposing yourself to the sun or temperatures higher than 25 C DOES NOT prevent the coronavirus disease (COVID-19).”

But UV Does Kill Germs. Remember SODIS?

Solar disinfection (SODIS) of water in Indonesia using clear PET plastic beverage bottles. (Image courtesy of SODIS Eawag.)
Solar disinfection (SODIS) of water in Indonesia using clear PET plastic beverage bottles. (Image courtesy of SODIS Eawag.)

The idea of ordinary sunlight killing germs—all sorts of bacteria, viruses, fungi and protozoa—may have picked up steams from the solar disinfection of drinking water (SODIS). Leaving unfiltered and untreated water in plastic bottles (polyethylene terephthalate, or PET) is a simple, cheap and effective method of producing drinkable water promoted by NGOs in regions with few water treatment operations but abundant solar radiation, such as in Asia and Africa. SODIS has considerable success against bacteria, particularly E. coli, possibly due to the matchup of the wavelength of UV-A to the size of bacteria.


[i] Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1, New England Journal of Medicine, April 16, 2020.

[ii]The Reality Bubble, Blind Spots, Hidden Truths, and the Dangerous Illusions that Shape Our World, Ziya Tong, 2019.

[iii] Photoprotection in Ethnic Skin in Ethnic Skin, Dermatologica Sinica, December 2014 References How UV Light May Protect Us from the Coronavirus, Amina Khan, LA Times, April 14, 2020 Sunlight’s Ultraviolet Wavelengths Have Strengths, Limitations in Disinfecting Against The Coronavirus, Jessica Seigel, April 24, 2020.

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