TORONTO -- Ultraviolet light is getting a lot of attention when it comes to disinfecting and reusing masks that medical workers need to safely do their jobs. That’s because one segment of UV light is extremely effective when it comes to killing microorganisms, including coronaviruses like the one that causes COVID-19.

But the idea making the rounds online that UV light could be used to disinfect hands, clothing or other household objects is either incorrect or dangerous, depending on what type of UV you’re talking about.

The World Health Organization (WHO) has warned that UV light should not be used as a disinfectant for the coronavirus. “UV lamps should not be used to sterilize hands or other areas of skin as UV radiation can cause skin irritation,” the agency said.

The WHO also dismissed the idea that sun exposure or temperatures over 25C prevent COVID-19.

“You can catch COVID-19, no matter how sunny or hot the weather is. Countries with hot weather have reported cases of COVID-19. To protect yourself, make sure you clean your hands frequently and thoroughly and avoid touching your eyes, mouth, and nose.”


A quick lesson: the sun produces a spectrum of UV light. UV-A makes up the vast majority of the UV radiation reaching Earth and can penetrate deep into skin, causing aging such as wrinkles and age spots. UV-B more deeply damages the DNA in skin, leading to sunburn and eventually skin cancer.

UV-A and UV-B, the spectrums found in tanning beds or a wide variety of UV lamps and wands marketed to consumers, have virtually no effect on bacteria and viruses, says experts.

But a short-wave spectrum called UV-C is much more dangerous to all genetic material. It’s a germicide, which means it can kill up to 99.99 per cent of bacteria and viruses. The UV-C emitted by the sun is stopped by the ozone layer, so we aren’t directly exposed to it. That’s a good thing because our fragile skin and eyes couldn’t handle it.

When produced artificially, UV-C breaks up the genetic material of the pathogens floating in air or water and sticking to surfaces so that they cannot function or reproduce.

“All bacteria and viruses tested to date (many hundreds over the years, including other coronaviruses) respond to UV disinfection,” according to the International Ultraviolet Association (IUVA). “Some organisms are more susceptible to UV-C disinfection than others, but all tested so far do respond at the appropriate doses.”


The disinfection power of UV-C has been known for more than 100 years and is widely used to purify water, air and surfaces. A crisis such as the one gripping the globe can serve to push research and innovation that will ultimately lead to better technology, says Bill Anderson, a chemical engineering professor at the University of Waterloo who has expertise in UV disinfection.

In China, UV-C has been used to disinfect money, buses and elevators, in addition to widespread uses in hospitals.

“China has seemed to be ahead of the curve when it comes to UV disinfection, so it’s not surprising they’ve used it so extensively,” said Anderson.

He says UV is “quite promising” as a means to safely reuse badly needed N95 respirators. He is working with Prescientx, a Cambridge, Ont.-based company that is building a machine to disinfect up to 500 of the heavy-duty N95 masks an hour using UV light

Many hospitals already routinely use UV-C in air handling systems, or augment other cleaning and disinfecting methods with portable UV-C lamps or robots deployed to disinfect surfaces in rooms, or to disinfect medical tools like stethoscopes.

But the use of UV-C in medical settings is only a decade or two old, and up until this current crisis, it hasn’t been used on gowns or masks because hidden crevices and folds make it hard for UV light to work on pathogens. It’s also not really known how repeated exposure to UV-C will affect the materials in masks.

“The best thing is not to have to do it at all because you can never guarantee 100 per cent complete disinfection. But if new masks can’t be found when they’re needed, this is the next best thing,” said Anderson.


The wide variety of lamps and wands aimed at consumers that claim to disinfect electronics, keyboards, sheets and towels, some selling on Amazon for as little as $45, are “almost completely ineffective,” said Anderson.

“If you can safely look at these lights and be in the room with them, they are not powerful enough to kill COVID-19,” echoed Taylor Mann, whose Toronto-based company produces disinfection units for mobile devices.

On the other hand, exposure to UV-C light causes serious burns and eye damage within seconds.

“To stick your hands in a UV-C device is inviting melanoma. Any exposure to skin is very dangerous, and the effect on eyes is even worse,” said Anderson.

The IUVA also “urges consumers to exercise caution” when buying UV equipment. Look for third-party validation, as well as certification of materials and components by international standards organizations such as NSF, UL, or CSA.


UV-C is no “silver bullet” for disinfection, but it is extremely effective at zapping the germs found on mobile phones, says Mann, co-founder and CEO of CleanSlate.

Mann says his company’s system is deployed to clean mobile devices of workers, patients and visitors in 80 hospitals in Canada, the U.S. and internationally. He says adoption was already growing rapidly before COVID-19 emerged as a threat, but orders have skyrocketed 1,500 per cent between February and March.

The device is about the size of a desktop printer and is usually placed in hygiene touchpoints such as entrances to buildings and departments and nursing stations.

“Hospital staff frequently wash their hands but then they immediately touch their phones, which is one of the dirtiest things you could ever touch. That undermines hand hygiene,” Mann said.

“Your phone is your third hand that you never wash.”

There is plenty of research that shows just how germ-infected mobile phones can be, including with strains of bacteria that cause serious hospital-acquired infections. And it’s believed that the novel coronavirus responsible for COVID-19 can live on non-porous surfaces like phones and tablets for up to four days.

The CleanSlate device takes 20 seconds to fully disinfect three to four smartphones at once or one large tablet.

Mann says his company’s target has been health care but there is exploding interest from a range of sectors, including hospitality, education, manufacturing and corporate offices.

“There could be devices at the entrances to malls or at airports. But they have to be effective and fast. To get people to change their behaviour, you have to integrate the technology into their daily lives,” said Mann, a self-confessed germaphobe who co-founded the company in 2014 while at Queen’s University.

“I think this crisis has brought forward broad recognition that phone hygiene is an issue everywhere.”


A study published in the journal Nature in 2018 raises the potential for even more effective UV-C disinfection to prevent or reduce airborne viral infections that doesn’t risk human health. Though research needs to be done in real-world conditions, the scientists at the Columbia University Medical Center say the so-called far-UV-C spectrum could potentially lead to widespread decontamination efforts in public spaces, such as hospitals, doctors offices, schools, airports and airplanes.

“Continuous very low dose-rate far-UVC light in indoor public locations is a promising, safe and inexpensive tool to reduce the spread of airborne-mediated microbial diseases.”