Can you kill Coronavirus with UV light?

There’s only one type of UV that can reliably inactivate Covid-19, and it;s extremely dangerous. “The amount of energy needed to inactivate Covid-19, you would literally have to fry human beings.”

Recently, as the global anxiety about Covid-19 has reached extraordinary new heights, we have been asked some unusual requests from people and the industry. We had an enquiry from a individual about our equipment, saying, “Well, why can't we just get one of your UV lights and put it at the entrance of our factory? People can stand under it for a few seconds before they go in,” he asked.

Among the abundant “health” advice currently swarming around the internet, the idea that you can disinfect your skin, clothing or other objects with UV light has proved extremely popular.

So is this a good way to protect you from Covid-19? And is it true that since “the new Coronavirus hates the sun”, sunshine will immediately kill it, as some reports on social media have claimed?

In short, the answer is NO, NO, NO, and here’s why.

Sunlight contains three types of UV. First there is UVA, which makes up the vast majority of the ultraviolet radiation reaching the earth’s surface. It is capable of penetrating deep into the skin and is thought to be responsible for up to 80% of skin ageing, from wrinkles to age spots.

Next, there’s UVB, which can damage the DNA in our skin, leading to sunburn and eventually skin cancer (recently scientists have discovered that UVA can also do this). Both are reasonably well known, and can be blocked out by most good sun creams.

There is also a third type, UVC this relatively obscure part of the spectrum consists of a shorter, more energetic wavelength of light. It is particularly good at destroying genetic material – whether in humans or viral particles. Luckily, most of us are unlikely to have ever encountered any. That’s because it’s filtered out by ozone layer in the atmosphere long before it reaches our fragile skin. Or that was the case, at least, until scientists discovered that they could harness UVC to kill microorganisms. Since the discovery of UV light in 1878, artificially produced UVC has become a staple method of sterilisation, one used in hospitals, airplanes, offices, and factories every day. Crucially, it’s also fundamental to the process of sanitising drinking water. Some parasites are resistant to chemical disinfectants such as chlorine so UVC provides as a failsafe solution.

Though there hasn’t been any research looking at how UVC affects Covid-19, specific studies have shown that it can be used against other Coronaviruses, such as Sars. The radiation warps the structure of their genetic material and prevents the viral particles from making more copies of them. As a result, a concentrated form of UVC is now on the front line in the fight against Covid-19.

In China, whole buses are being lit up by the UV blue light each night for disinfection, while UVC-emitting robots have been cleaning floors in hospitals. Banks have even been using the light to disinfect their money.

UVC is really nasty stuff, you shouldn't be exposed to it. “It can take hours to get sunburn from UVB, but with UVC it takes only a few seconds.” If your eyes are exposed to UVC at the energy levels required for disinfection, it could cause severe or permanent damage.

To use UVC safely, you need specialist equipment and training. The World Health Organization (WHO) has issued a stern warning against people using UV light to sterilise their hands or any other part of their skin.

Recently, scientists have discovered a promising new type of far UVC which is less dangerous to handle, and still lethal to viruses and bacteria. This far UVC has a shorter wavelength than regular UVC. Far UVC experiments with human skin cells in the lab have shown that it doesn’t damage their DNA (however more research is needed to be sure).

On the other hand, bacteria and viruses won’t come off as well, because they are small enough for the light to reach.

However, the vast majority of the UVC lamps in the market don’t use far-UVC yet, and again, it has not been tested on humans, testing has only been done on cells in petri dishes and other animals, so this type of radiation probably won’t help during the current pandemic either.

Sunshine solution?

Would UVA or UVB work instead? And if so, does this mean you can disinfect things by leaving them out in the sun?

The short answer: possibly yes, but you wouldn’t want to rely on it.

In the developing world, sunlight is already a popular means of sterilising water; it’s even recommended by the World Health Organization (WHO).

The technique involves pouring the water into a clear glass or plastic bottle, and leaving it out in the sun for six hours. It’s thought to work because the UVA in sunlight reacts with dissolved oxygen to produce unstable molecules such as hydrogen peroxide, the active ingredient in many household disinfectants, which can damage pathogens.

Without water, sunlight will still help to disinfect surfaces, but it may take longer than you’d think.

The problem is we don’t know how long, because it’s still too soon for many studies to have been done on the new Coronavirus. Research on Sars — a close relative of Covid-19 — found that exposing the virus to UVA for 15 minutes had no impact on how infectious it was. However, the study didn’t look at longer exposures, or UVB, which is known to be more damaging to genetic material.

Another study found that the longer the flu particles were exposed to sunlight and the more concentrated it was, the less likely they were to remain infectious. Alas, the study looked at flu suspended in the air, rather than dried onto objects.

No one knows how long it takes to deactivate Covid-19 with sunlight, or what strength is needed. This entire means that using sunlight to disinfect surfaces is extremely problematic.

First of all, no one knows how long it takes to deactivate Covid-19 with sunlight, or what strength is needed. And even if they did, the amount of UV in sunlight varies depending on the time of day, the weather, the season, and where in the world you live, especially which latitude, so this wouldn’t be a reliable way to kill the virus.

Finally, it goes without saying that disinfecting your skin with any kind of UV will lead to damage, and increase your risk of skin cancer. Besides, since ultraviolet light is invisible and one will never realise that they are looking at something strong enough to damage the eyes as the damages is realised a few hours after exposure to this radiation and by this time, the damage is done.

Once the virus is inside your body, no amount of UV is going to kill the virus. Don’t fall prey to people and companies promising you to kill the Covid-19 with a UV lamp. If the lamp is not powerful enough to harm your skin and eyes it is not powerful enough to kill the virus. Request proper documentation, certification and test reports before you decide what to buy.

Q&A with Abhay Datta

Is it advisable for items to be placed in the sun? Do sun rays help in combating virus on the surface of the various items?

Yes, sunlight has the necessary UV energy to neutralise bacteria under prolonged exposure. It will also depend on the time of the day and month in the year to determine the exposure time.

Will items in malls and marts be treated with UV light before they are placed on the shelf? Or a specific highly controlled UV ray treatment?

All portable devices and electronic items, including mobile phones keys and other person effects can be treated with UV light to kill the bacteria. It is not practical to put everything in a mall under UV light. Personal belongings have a very small chance of spreading the virus because they are for personal use only. Items which are likely to be shared with others should be disinfected and ultraviolet radiation is one of the available sources.

Is this an opportunity for our industry to come up with a “new" type of packaging solution ...

Packaging has always been known to be a low carrier of virus. In the future maybe there could be some specific coating which could kill the bacteria. However, it will take a long time to test the viability and reliability of these coatings. It will also have to be seen that these coatings do not cause food contamination.