Can ultraviolet light kill the novel coronavirus during the pneumonia pandemic?

• Zaria Gorvett

Dan Arnold incredulously laughed, saying, "People would get roasted like this."

Arnold's ultraviolet technology (UV Light Technology) company supplies UV disinfection equipment to hospitals, pharmaceutical companies, and food producers. He has recently received a variety of inquiries, with many people wanting to know if UV can kill viruses and how to do it safely.

Some asked whether UV disinfection equipment could be placed at supermarket entrances, allowing people to stand under the light for a few seconds to get disinfected.

There is also widespread discussion on the internet about using UV to disinfect skin, clothing, or other items. It was reported that a school in Thailand has set up a tunnel with UV lights, requiring students to pass through the tunnel for disinfection before entering the school.

So, is UV a good way to protect us from infection? Is it true that strong sunlight can also kill viruses?

In short, the answer is no, let's see why.

Three Types of Ultraviolet

Sunlight contains three types of ultraviolet rays. The first is ultraviolet A (UVA), most of the UV radiation that reaches the Earth's surface falls into this category, and it can penetrate our skin, causing skin aging, wrinkles, and spots.

The second type is ultraviolet B (UVB), which can damage the DNA in skin cells, leading to sunburn and potentially triggering skin cancer. Recent studies have shown that UVA may also contribute to carcinogenesis. Applying sunscreen can help block both UVA and UVB rays.

The third type is ultraviolet C (UVC), which has a shorter wavelength and is more dangerous, capable of killing DNA material in human and viral molecules. Fortunately, we are not exposed to UVC rays because the Earth’s ozone layer blocks them.

However, since 1878, humans have found ways to produce UVC for sterilization, and now hospitals, airplanes, factories, and many other places use UVC for disinfection every day. UVC is also used in the drinking water disinfection process to ensure the destruction of parasites resistant to chemicals like chlorine.

The effect of UVC on the novel coronavirus has not been studied yet, but past research suggests that UVC can be used against other types of coronaviruses, such as the SARS virus. UVC radiation damages the genetic material of viral molecules, rendering them unable to reproduce.

Thus, UVC has become a hero in the fight against epidemics; in China, whole buses are irradiated with eerie blue light, hospitals use UVC to disinfect floors, and banks use UVC to disinfect coins.

The Dangers of Ultraviolet

However, exposure to UVC carries certain risks.

"It takes hours for UVB to cause sunburn, but UVC can cause damage in just a few seconds. If your eyes are exposed to UVC... do you know the stinging sensation of looking directly at the sun? The power of UVC is more than 10 times that."

Using UVC requires specialized equipment and training, and the World Health Organization has issued severe warnings against using UVC to disinfect hands or any part of the human body.

Recently, scientists discovered a new type of UVC—Far-UVC, which can kill viruses and bacteria but is not as dangerous to humans. Far-UVC has a shorter wavelength than typical UVC, but experiments show it does not damage the DNA of human skin cells (more research is still needed on this).

On the other hand, the sterilization efficacy of Far-UVC is also weaker because the light cannot reach some very small bacteria and viruses. Research has shown that Far-UVC prevents superbug MRSA infections in mouse wounds and can kill airborne influenza viruses.

However, currently, scientists are only placing human cells in petri dishes for study and are not directly exposing human bodies to Far-UVC. Given the current novel coronavirus epidemic, the efficacy of Far-UVC may be limited.

Sun Exposure for Sterilization?

So, can direct exposure to sunlight disinfect? In short, it is possible, but it is practically difficult to achieve.

Some developing countries have already used sunlight to disinfect water, and the WHO recommends doing so. Pour water into a clean transparent cup and place it under the sun for six hours; the interaction between UVA and dissolved oxygen in water produces unstable hydrogen peroxide, which can destroy pathogens.

Sunlight can also disinfect surfaces of objects, but the problem is we do not know how long the exposure should be. For example, in the case of the SARS virus, 15 minutes of sunlight exposure has no effect on the virus's infectivity.

What about the common flu virus? Scientists in Brazil found that during crop burning, sunlight is obscured by thick smoke, and at this time flu cases increase. But scientists believe that it is the flu virus in the air that is not being exposed to sunlight, not viruses on surfaces.

No one knows for sure how long to stay in the sun to kill the novel coronavirus, and besides time, there are other variables, such as where you are sunning, what season it is, and what time of day you are in the sun. Therefore, sun exposure for disinfection is not a reliable method.

Moreover, sun exposure can damage human skin and increase the risk of skin cancer. Once a virus enters the body, additional ultraviolet exposure is useless.

Article reproduced from: https://www.bbc.com/zhongwen/trad/science-52143162