[notyourday]

There's still no evidence that wearing masks reduces infection risk to the wearer. There is evidence that wearing masks reduces infection risk to those around the infectious wearer of the mask. It is, incidentally, the exact reasons surgeons wear masks -- not to protect themselves from a patient but to protect a patient from themselves.

[malandrew]

While it may not prevent you from catching the disease, it's pretty much a certainty that it will help mitigate the initial infectious dose you experience if you are exposed. A low initial infectious dose buys your immune system more time to learn to produce antibodies.

[notyourday]

There's no evidence for this to be the case. If we are going to go into "It is common sense to do X" then why stop at "it is a common sense, wear a mask" and not include "It is common sense, if you have co-morbidity then it is you job to self-isolate and let the others to continue to function"

[pariahHN]

How would someone build a physical filter that only works in one direction? I'm having some trouble finding good sources on air filter design, I did see some mentions of differing porosity on different sides looking at HVAC filters but unfortunately no details on the mechanisms/principles behind it. Most of the information I have seen regarding lack of mask effectiveness comes from mask type, improper use, and conservation of supply for those most in need, not the actual mask itself, implying that masks are in fact effective if they are used properly, with effectiveness depending on mask design - your comment appears to be referring to use in general.

I would think however that placing any physical barrier in the path of an airflow is going to have an effect regardless of direction, as some non zero portion of particles are always going to impact the barrier.

Edit: It appears from other comments you may in fact be referring to improper use of masks that are also not specifically designed to maximize filtration ability. I would still submit that some degree of mitigation is better than none, but I can see how a false sense of safety could outweigh the benefits of the mask.

[ardy42]

> There's still no evidence that wearing masks reduces infection risk to the wearer. There is evidence that wearing masks reduces infection risk to those around the infectious wearer of the mask. It is, incidentally, the exact reasons surgeons wear masks.

I think I agree with you, but the conversation about the personal protective value of masks has become so confused that it's very difficult to discuss. You've got people counting N95 respirators as "masks," it's almost always unclear what statistic a commentator is focusing on, and then there's anger (justified or unjustified) about the evolution of the CDC recommendations for the general public.

Could you clarify your position a bit?

[notyourday]

I'm in NYC. Anecdotally from going out at least half of the people do not wear them correctly. Mostly the nose is not covered. This is not the case just outside, it is also the case for mask wearers inside the stores.

In my view public wearing masks is social signaling. I find it disappointing that CDC decided to change its message on masks under pressure from "do something!" crowd.

What contributed to the crazy spread of COVID in NYC initially and what continued to contribute the spread after the stay at home order was NYC mass transit, especially the subway. The number of people using the subway now dropped but the trains are still fairly packed early in the mornings and late in the evenings as MTA has been cutting the frequency of trains.