The Best Mask or DIY Face Covering for COVID-19"
Cloth face coverings are no substitute for actual masks,
but may be better than nothing. Let me show you a few studies.
This study, testing the efficacy of various homemade masks,
found that scarves, pillowcases, and 100% cotton t-shirts were
probably the most suitable household materials, blocking
various bacteria and viruses at about 60% as well as surgical masks.
As you can see, the average filtration efficiency was about 90% or more
with surgical masks, compared to more like 50, 60, or 70%
for the improvised fabrics.
Vacuum cleaner bags worked better, right up there alongside
surgical masks, but were considerably harder to breathe through,
rendering it unsuitable for a face mask, and the same with tea towels.
Engineers at the University of Cambridge looked at 20 different options
compared to surgical masks. So you can see, for example, that lightweight
t-shirts have less than half the filtration of heavy weight cotton tees.
As you can see, windbreakers and denim jeans are right up there
comparable to surgical masks, alongside side the vacuum cleaner bags,
but suffer the same problem: they're very difficult to breathe through
and are thus ill-suited for face mask construction.
Taking that balance between breathing and filtration into account,
the most suitable fabrics for face mask construction may include
something like cotton flannel, though in a pinch a single sock pressed tight
against the nose and mouth might make a good emergency mask substitute.
Regardless of which you use, try not to touch the front of the mask
while you're wearing it or when you remove it, then wash your hands.
And cloth face coverings should be washed regularly.
Even though face coverings are intended to protect others
from the wearer, rather than the wearer from others,
masks have been recommended for self-protection during
the last pandemic for those at high risk in unavoidably crowded settings.
In hospital settings, for example, mask wearers appeared to have
been comparatively protected from contracting SARS.
However even three or four layers of cloth, in the form of cotton
handkerchiefs, only filter a fraction of what a simple surgical mask can block.
These are penetration numbers, so 4 layers of cotton may only block 4%,
10 times less than a simple surgical mask.
Improvised masks didn't seem to help in 1918, attributed
to the fact that to get the necessary protective filtration,
so many layers of gauze had to be used
that breathing was difficult and air leaked around the edges.
An improvised face mask should be viewed as the last possible alternative
if a supply of commercial face masks is not available.
The World Health Organization still doesn't think routine mask-wearing
in public is necessary, expressing concern that it might lead to
a false sense of security and neglect of more important measures
such as hand hygiene and social distancing, and may lead
to touching one's face. On the other hand, one could imagine
how wearing a mask might prompt people to avoid touching their face.
Gloves could play a similar role. Seeing bright purple gloves
on your hands can serve as a constant reminder.
Here's me recording the audiobook to "How to Survive a Pandemic."
Yes, you can still breathe in virus while wearing a mask
and you can still contaminate yourself with gloved fingers, but
anything that keeps you constantly conscious about the position
of your hands and stops you from touching your face might help.
Speaking of self-conscious, if everyone wore masks in public,
symptomatic patients who definitely should be wearing them
wouldn't fear being singled out for stigma.
Of course, universal use of face masks in public during a pandemic
could only be considered if supplies permit.
Sadly, inadequate preparation, misuse, and hoarding have led
to a critical shortage of personal protective gear
for those on the front-line. That's why the CDC is recommending
cloth face coverings instead of surgical masks.
You know things are getting desperate when an editorial in the Journal of the
American Medical Association entitled
"Sourcing Personal Protective Equipment During the COVID-19 Pandemic"
includes as a proposed suggestion coffee filter masks.
Surgical masks are usually made out of paper with a gelatinous layer
and should be changed every 4 hours or when they become wet
with saliva or other fluid, whichever comes first.
Surgical masks, as the name implies, are typically meant to protect others,
as in the patient opened up on the operating table.
N95 masks, or N95 respirators as they're often called,
are the cup-like masks that fit tighter to the face.
They are intended to protect the wearer.
The WHO and CDC have conflicting guidelines as to what
healthcare workers should wear during routine care of patients with COVID-19.
The CDC, along with its European counterpart, recommends N95 respirators,
whereas the WHO suggests surgical masks are sufficient.
While part of the WHO's reluctance to endorse N95s may come out
of a sensitivity to the global scarcity of such resources, the underlying
transmission dynamics of the COVID-19 virus remain largely
unknown, so it's impossible at this time to say
which recommendation is right with any certainty.
The relative importance of direct respiratory spread for COVID-19
versus indirect contact via contaminated objects is unclear.
For other viral respiratory illnesses like the common cold,
breathing appears more important than touching.
That's what that arm brace study showed.
For example, in one rhinovirus experiment, only 50% of those
touching contaminated coffee cup handles became infected.
For the flu, the relative importance of transmission continues to be debated,
which is remarkable since we've known about the virus for nearly a century.
Note that N95 respirators only work at peak efficiency
if they conform completely to the face, so they aren't for everyone.
Even one to two days of stubble may significantly undermine
the necessary seal. This is an actual infographic from the CDC
showing which types of facial hair may or may not be suitable.
They also must be used properly.
In a laboratory setting, N95 respirators have been found to be very effective,
but out in the real world, a review of the best science
on preventing the spread of respiratory viruses found no evidence
that the more expensive, irritating and uncomfortable N95 respirators
were superior to simple surgical masks.
Not that N95s aren't better at filtration, but perhaps due to poor compliance.
I remember how uncomfortable they were when I was working
with tuberculosis patients. So that would support the WHO
recommendation that N95s aren't necessarily better in real world settings,
though with proper fitting and compliance, they'd presumably come out on top.
Even with the perfect mask sealed over your mouth and nose,
your eyes are still exposed,
leading to a suggestion that medical workers wear goggles.
Monkeys can apparently be infected by dripping the COVID-19 virus
into their eyes, but a retrospective study of SARS, at least, found
no documented cases of transmission to healthcare workers just because
they didn't use eye protection. Until we know more about the transmission
of this virus, it would seem prudent for those in close contact
with coughing patients to err on the side of caution and use both
eye protection, like at least a face shield, and N95 respirators.
During the SARS outbreak in North America, regular surgical masks
were initially recommended, but the advice switched to respirators
after doctors started dying.
Here's how N95 masks compare to various cloth face coverings.
Note these are graphs of penetration,
so you can see for an N95 mask there's less than 5% penetration.
So at the particle size at which an N95 mask blocks more than 95%,
a mask made out of a t-shirt blocks only about 10%, scarves about 20%,
sweatshirts about 30%, and towels closer to 40%.
It's interesting that the Hanes t-shirts are no better than
any of the other t-shirts, but the Hanes sweatshirts appeared
to have an edge for some reason.
Of course, the study was funded by Hanes — just kidding.