Note: This thread is related to #COVID19.

Follow the World Health Organization's instructions to reduce your risk of infection. Avoid the three Cs: Crowded places, Close Contact Settings & Confined spaces. Airborne aerosols play an important role in transmitting COVID-19.

- Avoid crowded places and limit time in enclosed spaces

- Apply social distance

- Air rooms by opening windows & doors

- Keep hands and surfaces clean, cover coughs & sneezes

- Wear a mask when you are not at home or when physical distancing is not possible


Medical face masks are less useful then N95 respirators, but not very much less so and better than nothing.

Even just cloth is better than nothing, if used properly.

Priority should be given to healthcare workers.

Info, references & disclaimer below.



2/ I looked at studies comparing medical masks and N95 respirators (references below).

I only considered those on the field (ie no mechanical analysis or use of machines; only PPEs worn by doctors in hospitals) and those with pathogens of size comparable to COVID-19.

3/ Of the 3 studies I found:
- Two reported no significant difference in effectiveness
- One says N95 way more effective

The last study is the only one reporting that participants were involved in high-risk procedures, whereas the others only reported use in proximity

4/ Citations:
-  via @StephenPiment
-  via @krystoferivanov

5/ Perhaps more importantly, this study(via @naval) shows that even t-shirts and scarves are somewhat effective, though very much less so than medical masks.

6/ It seems to me that there are only 3 valid arguments not to wear masks today, and that's only under the current situation in which supply is limited.
- Healthcare workers need them
- If personal supply is limited, you should use them only when the risk is higher.
- (continues)

7/ The last thing to be careful is that masks might induce self-harming behavior such as:
- touching your nose, lips or eyes because you sweat
- touching the exterior or their strings and then touching your nose, lips or eyes
- giving a false sense of security & making you go out

8/ Wearing a medical mask, or even a scarf:
- Is definitely not even close to being 100% effective
- Is better than nothing
- It's useful not only because it protects you, but especially because it protect others
- Shouldn't give a false sense of security

9/ I've read advice such as the below and I'm not in a position to say whether they are net positive or net negative, but I post it here for completeness (via @StephenPiment)

10/ All in all:
- Wearing any kind of PPE seems to be better than nothing if worn properly, but
- might have contraindications if unsafe behavior is adopted, so
- it's important you weight properly benefits and risks.

That said, I'm not a doctor and this is not medical advice.

11/ Some more info:


13/ If you have remarks, data points, studies, please let me know and I'll add them here if relevant.

14/ Some good points

15/ One additional reason why wearing a scarf is better than nothing if done properly, is that the more people wear something, the more *other* people are incentivized to wear something too, protecting the herd in a way which has less side effects than getting everyone sick.

16/ Also, this is just my personal guess based on my limited knowledge, but:

If you use scarves make sure to wash them at high temperature before reusing!

(30 Celsius is definitely not enough; I've read 60 Celsius for at least 30 mins)

In general (continues below)

17/ … in general, PPEs aren't safe to reuse unless sanitized, and some cannot be sanitized without compromising their effectiveness.


19/ More studies validating that medical face masks are effective



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