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This post has been updated. It was originally posted on April 10, 2020.
Follow all of PopSci’s COVID-19 coverage here, including how to make your own face masks, how to make your own hand sanitizer, and the latest stats of the sanitary crisis.
The Centers for Disease Control and Protection has encouraged people to wear masks at all times while indoors, even if you’re vaccinated. Besides keeping away from other people, they are “one of the most powerful weapons we have to slow and stop the spread of the [COVID-19].”
A growing body of evidence has proven that face coverings can help stop the respiratory droplets largely responsible for spreading the novel coronavirus from traveling through the air or coming into contact with other people. But in order for them to protect you and your community, you need to clean your mask regularly.
You can employ a number of methods to sanitize face masks but be warned—these are only good for killing viruses and bacteria on coverings made out of cloth-like cotton or polypropylene. If you happen to have some surgical masks and are trying to figure out how to reuse them, let us stop you right there.
“Surgical masks are made out of a really soft cloth that’s just a small bit stronger than a paper towel, and its components can be heavily damaged by some of the agents that you might use in the home,” says Rachel Noble, a microbiologist, and professor at the University of North Carolina at Chapel Hill.
Applying any of the following methods to surgical masks will unequivocally make them either less effective or entirely ineffective against airborne particles possibly carrying COVID-19. But if you do them right, they should thoroughly sanitize cloth masks.
How to disinfect a face mask by boiling it
An easy way to sanitize face masks is to let them sit in boiling water for five minutes. It’s as simple as that.
The downside is that depending on the cloth your mask is made of, a few rounds of boiling could damage it or affect breathability.
“Cloth face masks are going to have a lifetime—they deteriorate the same way your bedsheets fall apart wash, after wash, after wash,” says Noble.
To ensure your mask remains functional after boiling, you’ll need to inspect it closely—hold the mask up to a light source and check for any thin areas where a small hole might be forming. COVID-19 particles are only between 60 and 140 nanometers in diameter, which means they can slip right through any loosely woven or damaged fabric. To be on the safe side, Noble recommends not boiling your mask more than 10 times.
Toss reusable cloth face masks in the laundry
Tossing your face masks along with the rest of your laundry in the washing machine is a great way to sanitize them. Just as hand soap disintegrates the virus by breaking its exterior, your trusty detergent will be enough to leave your face masks ready for another use. Pay special attention to temperature, though, Noble says—it’s an added layer of protection.
Water heated to 140 degrees Fahrenheit has proven effective at degrading most viruses, and both the World Health Organization and the UK’s National Health Service recommend this temperature for treating contaminated clothes and fabrics. But because a 140-degree shower would burn your skin, most people’s water heaters are set to 120 degrees. “A lot of viruses will be inactivated at that temperature, but they won’t completely be obliterated,” Noble explains.
Some modern washing machines have internal water heaters that can push water beyond 120 degrees, but if you don’t have one of these, we still don’t recommend you change your water heater’s settings. Still, no matter what your machine is capable of, the most important component here is laundry detergent. Make sure you load your machine with the appropriate amount of soap and complement it with your laundry booster of choice: Chlorine, color-safe bleach, or OxiClean will provide some extra oomph.
Should there be any pathogens the machine didn’t kill during the washing cycle, you can be sure you’ll finish them off after five to 10 minutes at high heat in the dryer.
How to sanitize a face mask with hot water and bleach
If you’re still waiting to have enough clothes for a load of laundry, or simply do not feel like waiting for water to boil, Noble suggests soaking your face masks for five minutes in a solution of one teaspoon of bleach for every quart of hot water. Temperature doesn’t really matter—the bleach is doing the sanitation work—but it’s an extra layer of security.
[Related: How to make a face mask without a sewing machine]
You’ll need to be careful, though—using a higher concentration of bleach or leaving any of the corrosive chemical on the fabric after soaking could damage your mask. Also, since your face mask will be directly over your nose and mouth, you’ll want it to be clear of bleach when you put it on. Inhaling any residual fumes from it could damage your airways or worsen any respiratory condition.
To make sure you get rid of any leftover bleach, take the mask out of the solution and rinse it under the tap water for 10 to 15 seconds—any temperature. After that, soak it in clean water for another five minutes. You can hang your masks to dry or put them in the dryer at high temperature for some extra sanitization.
For extra-safe fabric masks, wait a week before rewearing—even after a hefty clean
Sanitizing face masks is one action where the premise “the more, the better” definitely applies. Each of the methods above will do on its own, but if you’re still wary or want to be extra sure you’re not running any risks, you can use time to your advantage, too.
COVID-19 particles have a limited life span depending on the surface they end up on, and even though we know how long the virus can live on certain materials, evidence points to time ranges, not absolute numbers, which makes it variable.
Still, studies have used larger samples of the virus that you’d normally find if someone carrying the virus sneezed on your groceries. The CDC has made it clear that even though it is possible to get infected this way, it’s still very uncommon, and efforts should be focused on mask-wearing and social distancing.
If you were to use time as your sole method of face mask sanitization, you would have to assume COVID-19 particles will be active for at least three to four days—the worst-case scenario. You’d have to leave your face masks in a secure place (like your basement) for that amount of time before thinking of reusing them. But even though the virus might waste away, bacteria and other microbes might fester.
That’s why, according to Noble, a good sanitizing combo would be to boil, wash, or bleach your face masks, then let them sit for a week.
Storage is just as important as sanitizing
Sanitizing your mask won’t change a thing if you don’t store it properly. Once you have a clean mask, put it in a closed plastic container or a new zip-close bag by itself.
If you want to go the extra mile, write on the bag or stick a note to the container with details about when you last sanitized the mask and the method you used. This will prevent cross-contamination and you’ll be able to tell for sure if the mask is safe to use or not.
How not to wash a face mask
You might have read about UV lights and are wondering why we didn’t include them on this list. Well, using them to disinfect masks is not as simple as it sounds.
First of all, you’d have to use the right kind of wavelength: UV-C, according to Noble. You can often find this kind of light in sterilization wands, but these come in a wide range of shapes, sizes, and prices, so it’s difficult to know for sure if they have been found to be effective against various pathogens—especially since we’re still learning about COVID-19 and its variants.
Also, face masks—whether they’re DIY or store-bought—have pleats and creases that allow the material to expand and cover as much of your face as possible. When UV light hits a mask, these folds become a problem.
“It is hard to get the entire surface of a mask properly irradiated,” says Noble. “The UV light is only going to degrade the viruses on the surface, not the ones in the shade.”
[Related: How to wear a face mask for maximum protection.]
That’s why although UV lights are widely used to sanitize personal protection items in healthcare and lab settings, this method is often complemented by other disinfection processes, such as bleach or hydrogen peroxide.
You may have also encountered people saying microwaving cloth masks is a fast and easy way to sanitize them. That is technically true, but it’s not as simple as just cooking your mask for a couple minutes, especially since some microwaves can catch certain types of cloth on fire.
Microwave settings are not standard, so it’s hard for any guide to account for the strength of each person’s microwave while also keeping them from burning small holes on their masks. And that’s not even considering that proper face masks have a metal noseband that definitely won’t play nice with your microwave.
To be on the safe side, we recommend you stay away from the microwave—a rule that also applies to reheating pizza.
Updated August 25, 2021, at 3pm: This story has been updated to more accurately reflect new guidelines for COVID-19 prevention released by the Centers for Disease Control and Prevention, and recent research on the spread and prevalence of COVID-19.
