I THINK YOU SHOULD WEAR A MASK. WHAT IT IS MADE OF MATTERS AND HOW YOU USE IT MATTERS.
As we get deeper and deeper into the COVID-19 wilderness there are many states, counties, and people on Facebook issuing mandates that we all wear masks when in public. With supplies of medical grade (surgical and N95) masks being inadequate to even meet the needs of hospital workers, many are sewing their own masks or even opting to wear bandanas.
If you find yourself in need of a mask but can't obtain a medical grade one or (rightly) want to reserve those supplies for the hospital, EMT, grocery, and restaurant workers -- what do you do?
Let's take a look at what we know and what we don't. Materials and Design
There are several groups testing common household materials for both ability to filter tiny particles from the air and breathability. Things from banana peels to bra cups have now been quantified and ranked. I'll spare you the lists and charts and discussions about brownian movement and cut right to the chase.
The best materials for home made masks are cotton + chiffon or cotton + silk or flannel
A bra cup is a relatively good choice (if you can breathe through it)
Coffee filters are bad choices
A single fabric layer (like a bandana) is also not a great choice
Anything is better than nothing
The sweet spot between breathability and filtration is some high thread count cotton paired with a chiffon layer. Stitching the layers together or making a cotton mask with a pocket for the chiffon or silk or flannel works just as well. A bonus is that these types of masks can be washed. Fit matters almost as much as material. If the mask is not very well fitted to the wearers face, it reduces the filtration by a striking amount. Take the gold standard, the N95 mask. Fitted with no gaps it filters somewhere between 85 and 99 percent of particles. If there is a gap in the face seal that number drops to 12 to 34 precent. The idea is that if the mask is not tight fitting, air (and virus) can flow through the gaps and skip the filtration altogether.
That brings us to the next point: What you do with the mask matters a lot. Behavior
It is critically important that you continue to practice physical distancing, fastidious hand washing, and try not to touch your face.
A mask does not make it ok to gather in groups or get closer than 6 feet to other humans. If your mask is washable you should wash it after every use. If it is not washable, you should throw it away and use a new one after every use.
Don't take your mask off and put it down on a surface you will later touch without washing. Your mask is contaminated.
The bottom line is that we don't have great evidence of any kind in this current pandemic and we have to go based on best available data and extrapolation. That data and expert (not me) extrapolation says that everyone should be covering their faces with something if at any risk of being exposed to another human. Stay home (if you can). Wash your hands. Don't touch your face. Wear a mask.
I am a registered dietitian. I have no formal epidemiological or public health training. I am just a very curious and evidence-oriented human. Listen to the experts.