 Cloth face coverings are no substitute for actual masks, but may be better than nothing. Let me show you a few studies. This study, testing the efficacy of various homemade masks, found that scarves, pillowcases, and 100% cotton t-shirts were probably the most suitable household materials, blocking various bacteria and viruses. About 60% as well as surgical masks. As you can see, the average filtration efficiency was about 90% or more with surgical masks, compared to more like 50%, 60%, or 70% for the improvised fabrics. Vacuum cleaner bags worked better right up there alongside surgical masks, but were considerably harder to breathe through, rendering it unsuitable for a face mask and the same with tea towels. Customers at the University of Cambridge looked at 20 different options compared to surgical masks, so you can see, for example, that lightweight t-shirts have less than half the filtration of heavy-weight cotton tees. As you can see, windbreakers and denim jeans are right up there comparable to surgical masks alongside the vacuum cleaner bags, but suffer the same problem. They're very difficult to breathe through and are thus ill-suited for face mask construction. Considering that balance between breathing and filtration into account, the most suitable fabrics for face mask construction may include something like cotton flannel, though in a pinch a single sock pressed tight against a nose and mouth might make a good emergency mask substitute. Regardless of which you use, try not to touch the front of the mask while you're wearing it or when you remove it, then wash your hands. And cloth face covering should be washed regularly. Even though face coverings are intended to protect others from the wearer, rather than the wearer from others, masks have been recommended for self-protection during the last pandemic for those at high risk in unavoidably crowded settings. In hospital settings, for example, mask wearers appear to have been comparatively protected from contracting SARS. However, even three or four layers of cloth in the form of cotton handkerchiefs only filters a fraction of what a simple surgical mask can block. These are penetration numbers, so four layers of cotton may only block to 4%, 10 times less than a simple surgical mask. Improvised masks didn't seem to help in 1918, attributed to the fact that to get the necessary protective filtration, so many layers of gauze had to be used that breathing was difficult and air leaked around the edges. An improvised face mask should be viewed as the last possible alternative if a supply of commercial face masks is not available. The World Health Organization still doesn't think routine mask wearing in public is necessary, expressing concern that it might lead to a false sense of security and neglect of more important measures such as hand hygiene and social distancing, and may lead to touching one's face. On the other hand, one could imagine how wearing a mask might prompt people to avoid touching their face. Gloves could play a similar role, seeing bright purple gloves on your hands can serve as a constant reminder. Here's me recording the audiobook to How to Survive a Pandemic. Guess you can still breathe in virus while wearing a mask and you can still contaminate yourself with gloved fingers, but anything that keeps you constantly conscious about the position of your hands and stops you from touching your face might help. Speaking of self-conscious, if everyone wore masks in public, symptomatic patients who definitely should be wearing them wouldn't fear being singled out for stigma. Of course, universal use of face masks in public during a pandemic could only be considered if supplies permit. Sadly, inadequate preparation, misuse, and hoarding have led to a critical shortage of personal protective gear for those on the front line. That's why the CDC is recommending cloth face coverings instead of surgical masks. You know things are getting desperate when an editorial in the Journal of the American Medical Association entitled Sourcing Personal Protective Equipment during the COVID-19 pandemic includes as a proposed suggestion, coffee filter masks. Surgical masks are usually made out of paper with a gelatinous layer and should be changed every four hours or when they become wet with saliva or other fluid, whichever comes first. Surgical masks, as the name implies, are typically meant to protect others as in the patient opened up on the operating table. N95 masks, or N95 respirators as they're often called, are the cup-like masks that fit tighter to the face. They are intended to protect the wearer. The WHO and CDC have conflicting guidelines as to what healthcare workers should wear during routine care of patients with COVID-19. The CDC, along with its European counterpart, recommends N95 respirators, whereas the WHO suggests surgical masks are sufficient. While part of the WHO's reluctance to endorse N95s may come out of a sensitivity to the global scarcity of such resources, the underlying transmission dynamics of the COVID-19 virus remain largely unknown, so it's impossible at this time to say which recommendation is right with any certainty. The relative importance of direct respiratory spread for COVID-19 versus indirect contact via contaminated objects is unclear. For other viral respiratory illnesses, like the common cold, breathing appears more important than touching. That's what that arm brace study showed. For example, in one rhinovirus experiment, only 50% of those touching contaminated coffee cup handles became infected. For the flu, the relative importance of transmission continues to be debated, which is remarkable, since we've known about the virus for nearly a century. Note that N95 respirators only work at peak efficiency if they conform completely to the face, so they aren't for everyone. Even one to two days of stubble may significantly undermine the necessary seal. This is an actual infographic from the CDC showing which types of facial hair may or may not be suitable. They also must be used properly. In a laboratory setting, N95 respirators have been found to be very effective, but out in the real world, a review of the best science on preventing the spread of respiratory viruses found no evidence that the more expensive, irritating, and uncomfortable N95 respirators were superior to simple surgical masks. Not that N95s aren't better at filtration, but perhaps due to poor compliance. I remember how uncomfortable they were when I was working with tuberculosis patients. So that would support the WHO recommendation that N95s aren't necessarily better in real-world settings, though with proper fitting and compliance, they presumably come out on top. Even with the perfect mask sealed over your mouth and nose, your eyes are still exposed, leading to a suggestion that medical workers wear goggles. Monkeys can apparently be infected by dripping the COVID-19 virus into their eyes, but a retrospective study of SARS, at least, found no documented cases of transmission to healthcare workers just because they didn't use eye protection. Until we know more about the transmission of this virus, it would seem prudent for those in close contact with coughing patients to err on the side of caution and use both eye protection, like at least a face shield, and N95 respirators. During the SARS outbreak in North America, regular surgical masks were initially recommended, but the advice switched to respirators after doctors started dying. Here's how N95 masks compare to various cloth face coverings. Note these are graphs of penetration. So you can see for an N95 mask, there's less than 5% penetration. So at the particle size at which an N95 mask blocks more than 95%, a mask made out of a t-shirt blocks only about 10%, scarves about 20%, sweatshirts about 30%, and towels closer to 40%. It's interesting that the Hanes t-shirts are no better than any of the other t-shirts but the Hanes sweatshirts appeared to have an edge for some reason. Of course, the study was funded by Hanes. Just kidding.