
Ask HN: Efficacy of homemade masks in reducing transmission? - VieEnCode
What is the current best research we have on the efficacy of homemade cloth masks against reducing the community transmission of COVID-19?
======
jjgreen
There is little evidence to support their use. The WHO's April announcement
stated

 _At the present time, the widespread use of masks by healthy people in the
community setting is not yet supported by high quality or direct scientific
evidence._

But the growing movement towards mandatory usage continues regardless of the
absence of evidence. This morning, the Head of the Royal Society was
interviewed on Radio 4 (the BBC's news channel). In response to a question on
the absence of scientific trials on efficacy, he responded that requests for
such were _methodological fetishism_ , a term I had only previously
encountered in the works of Deluze.

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open-source-ux
This research is from 2013:

 _Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza
Pandemic?_

Link to PDF: [https://www.researchgate.net/profile/Katy-
Anne_Thompson2/pub...](https://www.researchgate.net/profile/Katy-
Anne_Thompson2/publication/258525804_Testing_the_Efficacy_of_Homemade_Masks_Would_They_Protect_in_an_Influenza_Pandemic/links/53fefd8f0cf21edafd154e85/Testing-
the-Efficacy-of-Homemade-Masks-Would-They-Protect-in-an-Influenza-
Pandemic.pdf)

Summary:

> Several household materials were evaluated for the capacity to block
> bacterial and viral aerosols. Twenty-one healthy volunteers made their own
> face masks from cotton t-shirts; the masks were then tested for fit. The
> number of microorganisms isolated from coughs of healthy volunteers wearing
> their homemade mask, a surgical mask, or no mask was compared using several
> air-sampling techniques.

> Our findings suggest that a homemade mask should only be considered as a
> last resort to prevent droplet transmission from infected individuals, but
> it would be better than no protection.

Interestingly, tea towels (dish cloths) showed a higher level of filteration
than t-shirts in this study.

Edit: here is a more recent review of the scientifc literature on cloth masks
from the Royal Society in the UK. This is a pre-print - link is to PDF:

 _Face masks and coverings for the general public: Behavioural knowledge,
effectiveness of cloth coverings and public messaging_

[https://royalsociety.org/-/media/policy/projects/set-c/set-c...](https://royalsociety.org/-/media/policy/projects/set-c/set-
c-facemasks.pdf?la=en-GB&hash=A22A87CB28F7D6AD9BD93BBCBFC2BB24)

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rossdavidh
The efficacy of non-homemade masks is not as well demonstrated as one might
hope. It takes years to plan, execute, analyze, review, and publish a good
experiment, and there wasn't nearly as much interest in this question until a
few months ago.

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lmilcin
From what I have seen, the cloth masks' effectiveness is pretty much nil
except for following situations:

\- If you cough, it might stop large portion of droplets from propagating and
it will reduce the distance at which it initially travels.

\- As a constant reminder, it functions to prevent you from touching your
face, keep you more aware of what you are touching/doing and to pressure a
little bit other people to do the same.

This is my current understanding.

The real masks are actually pretty complicated things. For example, a lot of
effort is on ensuring the air does not travel AROUND the mask, greatly
diminishing its filtering ability.

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dgritsko
I think one benefit of homemade mask usage is simply that it helps to
normalize masks in general. Seeing others wear masks in various contexts can
help reduce the stigma of embarrassment that one might feel, or serve as a
helpful reminder to wear one.

~~~
nkurz
I don't think I understand your point. Are you saying that having more people
wear homemade masks provides "cover" for people who wear more effective
medical-grade masks? Or for people who want-to/need-to wear masks for non-
medical reasons? Which is to say, unless we accept in advance that masks are
effective at preventing the spread of disease, is there a reason that we would
want to "normalize masks in general"?

~~~
dgritsko
Yeah, I should've made it more clear - if they aren't "effective" then it
would be pointless to normalize them. Based on stuff like this[1] I happen to
think that they are, although exactly _how_ effective seems highly dependent
on a number of things.

[1]: [https://www.livescience.com/are-face-masks-effective-
reducin...](https://www.livescience.com/are-face-masks-effective-reducing-
coronavirus-spread.html)

------
VieEnCode
[Edit: if readers have relevant papers to share, I'd be very grateful.]

~~~
nkurz
Here's a New Zealand Health literature survey with lots of relevant links:

 _This paper summarises some of the evidence and policies around the use of
non-surgical non-N95 masks by the public and in clinical settings for the
purposes of reducing transmission of SARS-Cov- 2 /COVID-19._

[https://www.health.govt.nz/system/files/documents/pages/revi...](https://www.health.govt.nz/system/files/documents/pages/review_of_science_and_policy_around_face_masks_and_covid-19-15may2020.pdf)

