Masks and respirators for prevention of respiratory infections: a state of the science review

I recommend giving this a read when you have the time, it should hopefully answer any questions you have and better than I can.

An assumed droplet and contact mode of transmission leads to prevention policies that center on handwashing and surface cleansing, maintaining 2-m physical distancing, wearing medical masks (whose waterproof backing is designed to stop droplets) within that 2-m distance (especially when attending an infected patient), using physical barriers (e.g., plastic screens) and providing health-care workers with higher-grade respiratory protection only when undertaking AGMPs. However, if the virus is transmitted significantly by the airborne route, different prevention policies are needed, oriented to controlling air quality in indoor spaces (e.g., ventilation and filtration), reducing indoor crowding and time spent indoors, wearing masks whenever indoors, careful attention to mask quality (to maximize filtration) and fit (to avoid air passing through gaps), taking particular care during indoor activities that generate aerosols (e.g., speaking, singing, coughing, and exercising), and providing respirator-grade facial protection to all staff who work directly with patients (not just those doing AGMPs)

This is why I specified N95 respirators in my first comment. If you are unfamiliar, N95 is a NIOSH air filtration rating, which is used to describe the ability of a respirator to protect the wearer from airborne solid and liquid particulates. The review I linked goes into more details on this as well. I recommended N95 or better specifically because Covid is the illness I’m most concerned with avoiding, and the evidence suggests that they provide meaningful protection over lower grade respirators or surgical masks. Another quote from the link above that stood out to me:

The certification of surgical masks for particle/bacterial filtering efficiency (P/BFE) does not reflect equivalence to respirators as the filtration is typically compromised by poor face seal. The ASTM F2100-21 P/BFE certification, for example, requires at least 95% filtration against 0.1-µm particles and at least 98% against aerosolized Staphylococcus aureus, but this is on a sample of the mask clamped in a fixture, not on a representative face. In terms of filtering aerosols, N95 respirators outperform surgical masks between 8- and 12-fold. The effectiveness of certified surgical mask material against transmission when used as a filter was demonstrated in a hamster SARS-CoV-2 model. Infected hamsters were separated from non-infected ones by a partition made of surgical mask material; when the partition was in place, transmission of SARS-CoV-2 was reduced by 75%.

In addition to protecting the wearer, respirators provide very effective source control by dramatically limiting the amount of respiratory aerosols emitted by infectious individuals. In one study, risk of infection was reduced approximately 74-fold when infected, and susceptible individuals both wore well-fitting FFP respirators compared to when both wore surgical masks.

As for one-way masking, well, it is unfortunately significantly less effective (from what I understand), and is a big part of why I’m so concerned by others not masking. I simply cannot avoid being around others all the time, and their lack of effort is directly endangering me and my wife. If it really all came down to personal choice, I wouldn’t care if people wanted to risk their health. Still, while I don’t have any studies or anything to link you at the moment specifically on the effectiveness of one-way masking, all I know is that I mask and don’t get sick, and they don’t mask and do get sick. It’s anecdotal, sure, and I’m certain the mask is not the only thing affecting this, but as far as I can see it’s the largest difference in our behavior. I’ve heard as well that wearing a respirator will reduce viral load should you be infected despite the filter, and so your sickness will be less severe, but I don’t have any evidence on hand for this.

Because the virus is transmitted via spittle/moisture from other people not wearing masks. The virus doesn't just hang out in the air on its own; it's suspended in aerosol particles.