UV light can kill viruses, but home devices risk false security, say experts

Researchers say hand-held ultraviolet light devices being sold online with claims they can disinfect groceries and clothing can be unreliable and dangerous if mishandled.

The UV light sanitizers are being advertised as the panacea for the COVID-19 pandemic, able to disinfect everything from dinner vegetables to doorknobs.

Many different models are being sold online, ranging in price from $25 to $200. An online search for those listed as top products on business and tech sites list 17 as sold out or "in high demand."

They look like a small flashlight or flat curling iron and often claim to kill 99 per cent of germs. In Canada such claims require scientific proof.

"If a company cannot provide scientific evidence [then] do not buy their product," said Taylor Mann, founder and CEO of CleanSlate UV in Toronto.

Mann said his UV supply business has exploded in popularity in the pandemic. He's moving manufacturing from China to Ontario, and pushing for tougher UV industry standards.

"There's a lot of devices out there that are very concerning," said Mann.

Canadian scientists researching the effectiveness of UV light as a disinfectant say the at-home technology is a poor defence against the coronavirus that causes COVID-19.

Ottawa researcher Richard Webster said the key to destroying pathogens is the intensity of the light, and he doubts consumer-grade devices are, in many cases, strong enough to disinfect within seconds, as some claim to do.

"We think the amount of UV you need is about 20,000 joules per metre squared and you probably aren't going to get that in your hand-held little device," Webster said.

His prototype device uses between 240 to 480 watts to achieve that dose of light.

Dubious claims

Webster is with a research team at Ottawa's CHEO Research Institute that reviewed 1,000 studies of UV light decontamination and is working on a way to disinfect medical masks so they can be reused.

He said industry and hospitals are collaborating on prototypes of UV light sanitizing devices across Canada. But he says those devices are not available, or recommended, for home use.

They are big and combine multiple strips of LED lights — more than could be housed in a handheld wand — that deliver a powerful blast of UV light.

The wavelength of the light emitted is potentially dangerous, so such sanitizers are usually housed in a box or cabinet and aren't turned on until they are fully enclosed. Although smaller versions often use the same LED lights as the hospital-grade versions, it's difficult to test their power, Webster says.

Claims that disinfection happens in seconds are questionable, Webster said, because it takes time to kill certain pathogens.

"I wouldn't use those as my first line of defence," said Webster.

It also takes shortwave UV-C light — with a wavelength of around 250 nanometres — to disinfect. Many of the consumer-grade models advertise that they do use that wavelength, but that in itself is a potential danger: UV light of that intensity can burn skin, damage eyes and cause skin cell mutations.

Ayman Yaghi, general manager of Arkalumen, the Ottawa company that built the prototype device designed to disinfect medical masks, says a hand-held consumer sanitizer using UV light is possible — but he would be reluctant to put one into service.

"The main concern is that the average consumer doesn't have the knowledge or skills to use the device effectively or safely," said Yaghi, who added that different viruses require different lengths of exposure to be neutralized.

He said he's wary of the specifications, claims and testimonials for the sanitizers sold online, some of which include images of the product being used to disinfect groceries and even masks.

Yaghi said he worries the devices will give a false sense of security to users.

"It's amazing that people in the comments on these products say that it works so well, but they don't really have a way to verify that it works on their groceries," said Yaghi.

Webster said grocery disinfection is best done with soap and water — or by just washing your own hands after touching packaging.

If a consumer does opt to wave an unproven UV light product over a cereal box for safety, Mann said the best-case scenario is it won't do anything.. 

"Worst-case scenario, you could be buying a product that is actively harming you. Realistically you should not be exposed to UV-C light that is powerful enough to make any kind of difference."