It should be understood that ‘surgical’ masks were never intended to protect the wearer from infection. They were designed to be used by people working in a sterile field (i.e. a surgical theater) to prevent the exhalation of droplets that could land on the patient and equipment. The primary concern in a sterile field is bacterial contamination and/or non-biological foreign particles because the body’s basic barrier to the environment (e.g. the skin) is open. Surgical masks made of impermeable polypropylene can limit the travel of exhaled droplets and provide protection to the mucosal surfaces in mouth and nose from the same but are in no way assured protection from aerosol contaminants; that is, particles that can remain suspended in stagnant air for many minutes. Common aerosols are cigarette smoke, perfumes, and the volatile organic compounds emitted by new plastics, all of which you can easily smell even wearing a tightly tied surgical mask because of the open gaps on the side.
Respirator masks like the N95-standard respirator are designed to make a good seal to the face, and provide reasonable protection for the wearer against aerosols for a certain period of time. The melt-blown polypropylene that N95 respirators are made out of stop small aerosols not by physically blocking them as that would also severely inhibit the flow of air but rather by drawing the air over electrostatically-charged fibers which grab the particles, and in the case of bacteria and virions, hold onto them until they desiccate and become inactivated. As the respirator becomes saturated with use, either from material inhaled through it or by moist exhalation, the effectiveness drops, hence why such items are considered to be ‘single use only’. A properly cared for N95 respirator that is not saturated with humidity can function effectively for many hours of use, and as long as it is allowed to dry can be reused for some period although with progressive degradation in filtering function.
Cloth masks are of marginal use in protecting users from aerosols or preventing their spread and I have yet to see a study that demonstrates otherwise with any kind of real control. My own casual experiment with improvised cloth barrier convinced me that they are of negligible utility for protection. There have been a number of studies purporting the utility of cloth masks in real world application based upon the difference in rates of infection between masked (cloth) and unmasked people but they do not account for differences in behavior that one might reasonably expect between someone who is taking the precaution of wearing a mask and someone who isn’t. I see the CDC guidance that someone cited above regarding woven cloth masks but I’ve frankly become somewhat dubious about the basis for that guidance and would personally not rely on a non-respirator mask indoors for protection.
Stranger