Coronavirus FAQ: How Do I Clean My Mask — Washing Machine? Oven? Broccoli Steamer?

Each week, we answer frequently asked questions about life during the coronavirus crisis. If you have a question you'd like us to consider for a future post, email us at goatsandsoda@npr.org with the subject line: "Weekly Coronavirus Questions."

Does putting a reusable mask in the oven for 30 minutes at 165 degrees Fahrenheit kill the virus that causes COVID-19 and other pathogens? If not, how do I clean it?

The good news: Yes, baking your cloth or synthetic mask would probably kill the SARS-CoV-2 virus that causes COVID-19. Several studies have shown that the virus dies when exposed to 158 degrees Fahrenheit for a length of time somewhere between 2 1/2 minutes and an hour.

The bad news: It may also singe your mask.

Remember, says professor Raina MacIntyre, head of the Biosecurity Research Program at the University of New South Wales' Kirby Institute, "An oven is designed to burn things!"

The jury is still out on exactly how important it is to wash your mask to prevent COVID-19 infection, but MacIntyre dug into some data from her 2015 study on cloth masks and found evidence that washing masks in a machine, instead of by hand, helps prevent infections of other seasonal viruses in health care workers. Her theory is that the longer wash cycle and hotter water temperatures in a machine kill viruses more efficiently than washing by hand.

In lieu of data specific to SARS-CoV-2, many experts said what we know from studies such as this one make it seem prudent to wash masks on a regular basis. And, certainly, laundering them does not hurt with the possible exception of shortening their life span.

Here's how experts advise you care for your masks (to the best of current knowledge, of course):

During the day: For those of us who now work from home, you're probably taking your mask on and off throughout the day. You don't need a new one every time you run an errand, but it's probably best to toss your mask in a clean plastic or paper bag to keep it free of debris when you're not wearing it. (We'll leave it up to you whether to zip the bag or not — some experts think it keeps contaminants out, but others worry about microbial growth.)

After a full day out of the house: The World Health Organization and the Centers for Disease Control and Prevention say that masks should be washed after a day's use. Based on her data analysis, MacIntyre agrees: "Both surgical and cloth masks get contaminated with viruses, so washing is really important," she says. "If you don't wash it properly, then it may not protect you, because the contamination gets greater and greater over time." After one day of use, her study showed viral contamination — though not with SARS-CoV-2, which hadn't yet been discovered. However, viruses can remain viable for days, she points out, and one recent study found that SARS-CoV-2 can live up to seven days on cotton. "The point is, if you put on an unwashed mask, you may be putting on a mask which is contaminated with viruses," she says.

In addition, WHO recommends taking care when removing your mask: "The wearer should be careful not to touch the outside of the mask. If the outside of the mask is touched during the removal process, the wearer must wash their hands immediately. Also, after removing the mask, the wearer should be careful not to touch their face until they can wash their hands."

MacIntyre suggests that laundering should happen in a washing machine if you have one, with the temp set to 140 to 194 degrees Fahrenheit (the hot setting on most machines).

One note: Check washing instructions before you buy. If you prefer to machine-wash, don't buy the type that requires hand-washing.

A mesh wash bag for delicate items may help protect masks from tearing in the machine.

MacIntyre recommends tossing masks in the dryer as well since that step can reduce the size of the pores in the fabric, which improves performance. And if your mask has a pocket for a filter, throw the filter away after using it once, she says.

Alternatives to the washing machine: If there isn't a washing machine in your home (or if you're avoiding a communal laundry setting during the pandemic), WHO advises hand soaking masks in cold water with .05% chlorine for 30 minutes, then rinsing them with water and laundry detergent. Air dry in a clean space — not on a dirty kitchen counter, for example. (Here's how to make .05% chlorine water.)

Sunlight could help, MacIntyre adds. This study showed that UVB light can kill SARS-CoV-2.

And if you're washing in a sink, Christopher Friese, nursing professor and director of the Center for Improving Patient and Population Health at the University of Michigan, reminds you to wash your hands before and afterward.

If you want to get creative, a steamer is another option, MacIntyre says. Wash the mask in the sink to get rid of any particulate matter, she suggests, and then place it in the compartment of the steamer where the broccoli usually goes. Heat water and steam the mask for five minutes. But be wary of doing this in the microwave — masks may have metal components that could be hazardous if microwaved.

If all of that sounds way too daunting, take heart from internal medicine physician Abraar Karan of Harvard Medical School, who notes there isn't data to confirm whether washing masks every day, or every few days — or even at all — reduces the transmission of COVID-19.

To be clear, he is in favor of washing masks. The potential benefits outweigh any harm ... not to mention the stink factor.

"When I leave work, I wear a cloth mask. And I wash that probably every few days; I have a couple I rotate between," he says. "You may want to wash it because of moisture or smell or dirt, but it's not like, 'Oh, I'm cleaning the COVID off of it.' "

When to retire a mask: Just like your favorite pair of jeans or T-shirt, you can keep using a mask as long as it holds its structural integrity. Follow Friese's morning routine: "Before I put it on, I inspect it and make sure it's not ripped or torn or has holes, and I make sure it's clean. If not, I throw it out or clean it." He also checks that it still fits on a regular basis: Put it on, take a deep breath and blow out, he says. "If it's feeling looser on your face, then it's probably time to retire it."

As for disposables: In general, follow the manufacturer's instructions, which usually recommend one day of use. If you're only using a disposable mask briefly while doing errands, store it in a bag and don't use it for more than eight hours total since it is designed for single use. You can even give it a light spray with an aerosolized disinfectant before you put it in the bag, MacIntyre says.

One last note: Wearing a mask reduces the risk of spreading COVID-19, but it doesn't eliminate it.

"We've got to hunker down," Friese says. "We're heading into very perilous times."

That's why Karan advises avoiding the 3 C's: crowds, closed spaces and prolonged, close contacts. That will help protect the people you live with and spend unmasked time with, he says.

When you do go out, do not skip the mask if you're worried it's not clean, Karan says. The most important thing you can do with a mask is wear it, he says.

Sheila Mulrooney Eldred is a freelance health journalist in Minneapolis. She's written about COVID-19 for Medscape, Mpls.St.Paul Magazine, Science News for Students and The Washington Post. More at sheilaeldred.pressfolios.com. On Twitter: @milepostmedia [Copyright 2020 NPR]