With the shortage of masks during the coronavirus outbreak, many people are wondering if washing masks is an effective way of cleaning them, to let you re-use them.
There are companies that claim to have washable anti-pollution masks. This company in India claims their mask is 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 tested this by washing a dirty 3M N95 mask our engineer Paddy 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 the mask was used for over a week, it still very captured 99% of particles. This fits with previous Smart Air results where 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 masks are made from. Many N95 and other pollution masks are made from 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.
Bottom line: Washing masks with soap and water decreases particle capture effectiveness. Washing is not a solution for extending mask lifespan.
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 masks claiming to be washable aren’t actually N95 standard masks, but just cotton masks that can be washed with potentially less damage to the fibers.
Another common so-called “washable” masks is made up of a washable cotton mask and a non-washable N95 filter.
Yet this filter still can’t be washed. 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 test above was for particle sizes that are the most likely to be affected by 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.
Looking for an effective way of cleaning your mask from viruses?
Coming soon: Check out this method of killing viruses without affecting mask performance!
Paddy is the CEO of Smart Air, running operations from Beijing. He’s has a Masters in aeronautical engineering from Bristol University, UK having specialised in aerodynamics. An advocate for open data, free information and transparent business, he spends his spare time promoting honest business and social enterprise.