With the shortage of masks during the coronavirus outbreak, many people are wondering if washing masks is an effective way of cleaning and re-using masks.
There are companies that claim to have washable anti-pollution masks. This company in India claims to have washable masks washable and can capture air pollution, bacteria, and “germs.”
Yet one thing that seems to be lacking is any actual data on this question–until now.
The Test: Washing Masks with Soap & Water
Smart Air engineer Paddy tested this by washing a dirty 3M N95 mask he had been using during the coronavirus outbreak.
Step 1: Use a Met One GT-521 laser particle counter to test what percentage of tiny 0.3 micron particles the mask filters.
Read more: Here’s why these 0.3 micron particles are they key for mask effectiveness.
Step 2: Wash in soap and water. Smart Air used Walch hand soap, which claims to remove 99.9% of bacteria, although it doesn’t say how effective it is at removing viruses.
Step 3: After drying overnight, test mask particle capture again.
Testing Mask Filtration Effectiveness
Although Paddy had worn the mask for over a week, it still captured 99% of particles. This fits with previous Smart Air tests that found masks retained effectiveness nearly unaffected after being worn 11 days, 20 days, and even 30 days.
However, washing the mask was much worse than natural “aging.” Washing decreased particle capture by 21%.
That is still better than the effectiveness of some surgical masks, but it’s a large drop.
Why Is Washing Masks So Harmful?
The answer to this question lies in the fibers companies use to make masks. To make N95 and other pollution masks, most companies use a mat of randomly aligned, very thin fibers.
Manufacturers then give these sheets an electrostatic charge.
See More: 3M explains static charge in masks in this video.
Washing removes that static electric charge, which decreases performance. Vigorous washing may also damage the fibers, making it easier for particles to pass through.
Why Do Some Companies Claim to Have Washable Masks?
Companies might not know that washing mask filter media can drastically reduce effectiveness. Or maybe the companies that claim to have washable masks know they aren’t actually N95 standard masks. For example, maybe they’re selling simple cotton masks that resist the damage of washing better, but are far less effective to begin with.
Another common type of “washable” masks use a washable cotton mask and a non-washable N95 filter.
Yet this filter still isn’t washable. What’s more, masks with replaceable filters tend to score worse on fit tests than 3M N95 masks. That pattern is clear in mask fit tests run by Beijing-based doctor Richard Saint Cyr.
Is Washing Masks with Alcohol Effective?
Perhaps another solution for washing masks is alcohol. If soap and water require rubbing, maybe alcohol will do less harm because it can disinfect without rubbing.
A group of researchers at the National Institute for Occupational Safety and Health tested N95 masks before and after dipping them in rubbing alcohol. After drying overnight, the masks captured 37% less particulate on average.
To be fair, this test exaggerates the harm. That’s because the researchers reported results for particle sizes most likely to “suffer” from alcohol treatment. Many masks capture particles in the range around 0.3 microns using fibers with static charge. Dipping in alcohol removes this charge.
However, when the researchers looked at even smaller particles, they found out alcohol sterilization did much less harm.
Read more: This is why the graph above makes no intuitive sense but is real.
Washing N95 masks with soap and water or alcohol decreases particle capture effectiveness.
Looking for an effective way of cleaning your mask from viruses?
This method kills viruses without affecting mask performance.
WHAT NEXT?
Along with wearing masks, air purifiers with HEPA filters are also one of the best ways to stay safe from a variety of pollutants in our air including viruses and dangerous PM2.5. A recent CDC study confirmed significantly lower COVID-19 infection rates in schools that used HEPA air purifiers. HEPA filters can significantly lower the risk of a variety of deadly diseases including diabetes, heart disease, cancer, and high blood pressure.
Read More: Four Steps to Choosing the Best Air Purifier
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What about fabric interfacing or used dryer sheets to add as a filter?
Footnotes to my other post: UV (sunlight) kills most everything – including COVID. (And us – use sunscreen!). Fresh air is always a good thing. Open windows as weather permits (unless there is a COVID patient coughing at the window you will not be letting virus in). And for the truly fastidious, natural fiber clothing (cotton) is better than synthetics as the virus dries out faster. A bag of ozone would kill yes, but not very practical/possible. Ozone kills you and your lungs while filling/opening the bag. I am hoping to spray something – even just isopropyl – on our… Read more »
I am a physician on the front lines looking for data on how to reuse masks because we are desperately short of supply – aggravated because of the hoarding by the general public. For whom the effectiveness is near zero beyond 6 feet (hence the 6 foot rule). You are 100 times more likely to contract by surface contact. (Hence the wash your hands and don’t touch your face/eyes rule). PLEASE follow these rules and donate your masks to your hospitals! Keep one if you must and reuse it for what should be rare trips into public spaces. Viruses do… Read more »
This article got me thinking (and Googling): What if we could make our own statically-charged masks? Your March 8 article talks about using two layers of the same material, but what about using two different materials that can cause a charge when rubbed together and washing and drying them without any fabric softener or dryer sheets? Would using one layer of wool and one layer of polyester have this effect? What about rubbing a balloon on a mask made of wool? For that matter, is there some way we can re-charge a 3M mask that has been washed? I don’t… Read more »
Thanks for this, very informative. Interesting to learn that masks are still effective after 30 days of usage. That’s about how long I usually use mine. What about spraying alcohol onto the outer surface of an N95/99 mask with a perfume type spray? I have been doing this on clothes and products after going shopping. I wonder if this would still remove the static charge, or if being sprayed rather than dunked would be less damaging? Probably the best solution though is to put your mask in direct sunlight after returning home when possible. I’ve been timing my shopping trips… Read more »