Can You Disinfect Your Face Mask With Sunlight? No, Says UV Expert

A University of Waterloo professor answers your burning questions.

As temperatures rise, the temptation to soak up the sunshine is strong. That’s a good thing, as there are plenty of physical and mental health benefits to vitamin D, thanks to the sun’s ultraviolet (UV) rays. Just make sure you’re basking in a physically distant manner. (We’re looking at you, overcrowded park visitors...)

Sunlight’s perks have been getting more positive attention recently, specifically in relation to COVID-19. But contrary to popular belief, the virus can still be spread, no matter how sunny it is outside.

A University of Toronto global study burst that bubble, as researchers found that warmer countries were just as susceptible to COVID-19 as colder countries.

A growing pandemic theory is that sunlight can kill the virus on face masks. This seems to stem from UV light’s sanitation properties: UV light technology has been used to disinfect everything from buses to hospitals and may be a promising tool to make personal protective equipment (PPE) reusable for doctors and nurses.

Watch: how does UV light work in killing coronaviruses? Story continues below.

So, should we be disinfecting COVID-19 prevention supplies with sunlight?

UV light expert Bill Anderson strongly advises against doing so. Leaving face masks, gloves, and face shields out in the sun won’t accomplish much, the University of Waterloo chemical engineering professor told HuffPost, and that has to do with how natural UV light works.

Sunlight lacks virus-killing element

The sun makes a spectrum of UV light, but there are three main types: UV-A, UV-B, and UV-C. Both UV-A and UV-B rays reach people’s bodies and can damage skin, leading to skin maturing faster and skin cancer. UV-C, on the other hand, gets mostly blocked out by the ozone layer. It’s a powerful wavelength, often referred to as the “germicidal UV,” Anderson said, as it can eradicate viral genetic material.

Think twice before hanging up your face mask on a clothesline or leaving it out to soak the rays: natural UV light is unlikely to sanitize a face mask. 
Think twice before hanging up your face mask on a clothesline or leaving it out to soak the rays: natural UV light is unlikely to sanitize a face mask. 

“It’s quite effective at killing viruses and bacteria. It does that by essentially messing up their DNA, which prevents them from functioning or reproducing,” he explained.

So, natural sunlight, lacking in UV-C, can’t kill COVID-19. He notes that UV-A and UV-B may make a small dent on a potentially infected face mask, but “it takes hours and hours” and doesn’t completely sanitize like UV-C does.

What about a sun-baked car?

Some believe that leaving a face mask on a car’s dashboard may magnify the sun’s ability to disinfect. But again, UV-A and UV-B rays won’t do much in this regard and Anderson said the windshield would actually reduce exposure.

Disinfecting cloth or disposable face masks on your car dashboard will expose your facegear to less, not more sunlight.
Disinfecting cloth or disposable face masks on your car dashboard will expose your facegear to less, not more sunlight.

What could potentially kill the virus is how hot the car gets, Anderson theorizes. SARS coronaviruses aren’t heat resistant, but this method isn’t scientifically proven and he worries this tactic would give false hope.

“My main concern is that people are fooling themselves into thinking they’re disinfecting their masks when they’re not,” he said.

If natural sunshine won’t work, how about a UV light device?

Consumer UV light devices are on the rise, with some claiming to kill all viruses on any surface.

But before you start scanning your face masks or groceries with a light bulb bought off Amazon, Anderson says they aren’t worth your money. Consumer UV light devices aren’t usually high-powered enough to be germicidal. Even if they are, it’s unlikely they’d be used correctly.

“You have to leave it on for minutes on end, which most people aren’t willing to do,” he said. “There are safety issues too, you can get burns or cancer from [incorrect use.]”

What’s more, a flat surface is easier to clean than something with crevices like a face mask, a University of Toronto press release points out.

Medical-grade UV light technology is more trustworthy, like that by Toronto-based company Clean Slate or Cambridge, Ont.’s Prescientix — both are among disinfecting product providers with track records for efficiency — but at the moment accessing these treatments is an unlikely option for the average person.

Instead, worried cloth face mask wearers may fare better with more conventional, well-tested cleaning methods like doing laundry.

How can I avoid a face mask tan line?

While less immediately health-related, the face mask tan line has kept many online stressed over their summer look.

In this regard, Anderson says age-old advice from dermatologists will come in handy: wear sunscreen and apply it regularly.

To fully curb the dreaded line, make sure you’re using a broad spectrum sunscreen. Sunscreen’s SPF is a measurement that determines how much UV-B gets blocked out and doesn’t take UV-A into account. Broad spectrum products offer protection against both wavelengths. SPF 15 to 30 is fine for most people, but SPF 50 might be ideal for those with sun-sensitive skin. Physical sunscreens are considered more environmentally friendly than chemical sunscreens, with early research published in the Journal of the American Medical Association suggesting they might be safer to use in the long-run too.

If you do get a face mask tan line, look on the bright side: These sun marks may be seen in a different light once summer hits its stride.