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Use at your own risk.
Using a home made mask may be ineffective at preventing any infection.
Most materials have not been tested by accredited laboratories for making masks. Using untested materials in masks may be harmful to your health.
Background Information...
What is COVID-19 and how do I protect myself?
Coronavirus 2019 (COVID-19) is a respiratory illness caused by a novel (new) corona virus [1]. It is most commonly spread from person to person in water droplets when a sick persons sneezes, coughs, or even talks, and some of these droplets reach a healthy person's mouth, eyes, or nose [1]. One way to protect yourself from others (if you're not sick), and to limit infecting others (if you are sick) is to place a barrier in front of your mouth, eyes, and nose. This is why healthcare workers wear face masks, face shields, and take other protective measures when treating patients [2].
How big is the virus that causes COVID-19?
The novel corona virus that causes COVID-19 is really small (0.06um to 0.14um -- um is an abbreviation for "micro meters", which are one millionth of a meter, or about 0.00004 inches) [3]. We're talking small... For comparison, the width of a human hair ranges from 17um to 181um [4]. A normal human eye can see objects as small as 100um [5]. Corona virus is at least 1000 times smaller than the smallest object you can see.
How can I stop the virus from getting into my mouth, eyes, and nose?
Stopping something that small from getting into your mouth, eyes, and nose can be tough. One way is wear a "shield" that blocks your entire face [6]. Not only does this add a barrier, but also helps keep you from touching your face, which may also be a way to catch COVID-19 [1]. Most shields still have gaps that could let water droplets in. This is where a mask helps add an additional layer of protection for your mouth and nose. Keep in mind... wearing a mask alone does not protect your eyes. If you are simply worried about infecting others (which we all should be!), a mask alone will help. If you are worried about becoming infected, you should wear a mask and a shield or glasses.
It's also important to recognize basic good hygiene behaviors that can help minimize your chances of catching COVID-19. These include: Avoiding close contact with people who are sick. Avoid touching your eyes, nose, and mouth with unwashed hands. Wash your hands often with soap and water for at least 20 seconds. Use an alcohol-based hand sanitizer that contains at least 60% alcohol if soap and water are not available [1].
Statistics and Dog Poop
Let's talk a little about statistics, and use an example we all should be able to visualize. If you own a dog, and have a yard, inevitably you'll have to deal with dog poop. Let's assume your dog is not trained to poop in a special spot, and tends to poop all over the yard. If you go walking in your yard, you probably can avoid the poop as long as there isn't a lot, and if you take your time to watch your step. If you're not paying attention (i.e. playing frisbee) and you're running around, it's more likely that you'll step on some poop, right? Now, imagine that poop is the novel corona virus, and you are paying attention and watching your step (following basic good hygiene behaviors), you can most likely avoid catching the virus (stepping on poop). This is what you can do in most daily situations.
What happens when you have more than one dog? Well, there's more poop, and you're more likely to step in some even when you're careful. This is where taking more time and being extra careful helps (or in the virus scenario, start wearing a mask and eye protection). When you go out in public, you can be extra careful by wearing a mask and eye protection.
What if you're a worker at a dog park, if all the dogs have diarrhea, and you have to run around all the time to break up dog fights? Now you're a front line medical worker and absolutely must have protection equipment so you don't get sick (step on poop). Now do you understand why it is so important for the medical workers to have proper protection gear?
The example so far only relates stepping on poop with you catching the virus. To fully understand the scenario, you're not a person any longer, you're a dog who poops. Wearing a mask is like putting a diaper on a dog. It will reduce the amount of poop, but we all know some poop will still get out (especially for the dogs with diarrhea).
Wearing a mask, eye protection, and following basic good hygiene behaviors all help reduce the likelihood of spreading and catching the virus. No guarantees, but definitely can help.
A bit about N95 masks
The bad news is none of the generally available masks are guaranteed to stop something the size of the novel corona virus. The good news is the virus doesn't tend to spread by itself, it spreads in water droplets [1], which are much larger than the virus, typically larger than 1um [7]. There's a lot of talk about "N95" masks being the ones to use [2][8], what are these?
The "N" stands for "Not oil resistant" and is a designation by NIOSH, the United States' National Institute for Occupational Safety and Health. It refers to the type of testing performed on the mask (these are United States' federal standards [9][10]). The test standards use a machine that generates particles of a certain size, attempts to pass these particles through the mask, and checks to see how many particles came through [11].
The "95" indicates that particular mask is 95% efficient when tested against the standards. The good news is the mask was able to filter out 95% of the particles in the test, the bad news is it didn't filter out 5% of them. Fortunately, the NIOSH standard test is for particles in the 0.3um to 0.5um size. Larger particles are filtered more efficiently. But... that's not part of the test, so technically we don't know how much more efficient. Since we're mostly concerned with water droplets that are at least 1um large, the N95 masks will do a pretty good job. An N95 mask should provide some protection against novel corona virus in water droplets.
Some N95 masks have an exhalation valve that makes it easier for the wearer to breathe. These will provide protection for the wearer. A sick person wearing this style of mask will continue to spread the virus. It is not recommended to use this style of N95 mask.
What about surgical masks?
Surgical masks are primarily designed to prevent large splashes and contaminants from reaching the nose and mouth, and limit the amount of water entering the environment by the wearer [8]. They have been shown to reduce the amount of novel corona virus introduced to the environment by an infected person [12]. However, it should be noted that there are conflicting research reports on the effectiveness of surgical masks against the novel corona virus [13]. And, to make things more complicated, there isn't a filter standard that surgical masks are tested against, and they could be anywhere between 10% to 90% efficient, depending on the manufacturer [14].
The current feeling is that surgical masks are better than wearing nothing and may help slow the spread of infection by those who are sick.
And finally, how about those DIY masks?
After the viral outbreaks in the mid-2000s, health officials became concerned that there could be shortages of protective masks in future outbreaks. Working with this idea, a design for a simple cotton mask was developed and tested for fit [15]. Cotton masks have been shown to be about 70% effective at filtering particles around 1um [16]. The same study concluded "Our findings suggest that a homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection" [16]. Due to the current limited availability of N95 masks, which should be reserved for medical workers, the general public may find itself in the "last resort" scenario.
The US Centers for Disease Control and Prevention (CDC) is providing a guide to make your own mask out of cotton [17]. [CDC eventually removed the coffee filter add-on to the bandana design... Leaving these comments in place as a historical record and warning...] One version contains the addition of a coffee filter as a layer. Sadly, the CDC does not provide the direct research links to validate their recommendations. Although we can infer their justifications though our own literature search for cotton, we have not found any research on the use of coffee filters [HELP NEEDED - IS THERE RESEARCH ON THIS?].
Multiple maker groups have been working on their own mask designs with various materials. The folks over at MakerMask.org [18] have come up with designs using a material called non-woven polypropylene. This material is used as layers in most surgical masks because it allows air flow while limiting the passage of water. We're not going to reproduce all of their information here, but the conclusion is to make masks using the reusable shopping bags found at most grocery stores [19]. This material has been shown to resist water penetration, but true particle filter testing results are not presented [HELP NEEDED - IS THERE RESEARCH ON THIS?].
Both cotton and non-woven polypropylene masks may be boiled for 10 minutes for sterilization. Cotton masks may also be washed (with soap) in a regular washing machine.
What about other materials?
Most materials have not been designed to have you breathe through them. Some materials "shed" particles that are hazardous to breathe and may cause longer term health problems. For example, we have found that landscape fabric is both a poor filter (it is specifically designed to let water through!), and sheds when air passes through it. HEPA filters have also been suggested as an option, but many of these also shed particles.
Besides shedding, some materials may perform very well at blocking particles, but may also resist air flow too much. Masks can build up carbon dioxide inside the "air box". Eventually, you may not be breathing in enough oxygen, and you may pass out (hopefully around someone else who can remove your mask...).
Some materials may also be treated with chemicals that are just bad to breathe or have in contact with your skin.
Due to the shortage of proper masks, and conflicting information from various sources, we are in the "Wild West" of mask making. Arsenic and radium (both very hazardous to your health) were used at one point in what we would call "quack medicine" today [20]. Let's try to be a little smarter and not have the COVID-19 pandemic masks be blamed for increases in lung cancers 15 years from now.
References:
1. https://www.cdc.gov/coronavirus/2019-ncov/downloads/2019-ncov-factsheet.pdf
2. https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control-recommendations.html
3. https://www.ncbi.nlm.nih.gov/books/NBK554776/
4. https://en.wikipedia.org/wiki/Hair%27s_breadth
5. https://www.wonderopolis.org/wonder/what-is-the-smallest-thing-you-can-see
6. https://www.delve.com/insights/face-shield-designs-to-fill-the-gap
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785820/
9. https://www.law.cornell.edu/cfr/text/42/84.181
10. https://www.cdc.gov/niosh/npptl/stps/apresp.html
11. https://youtu.be/-sY47zdE7YA
12. https://www.nature.com/articles/s41591-020-0843-2
14. https://blogs.cdc.gov/niosh-science-blog/2009/10/14/n95/
15. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373043/
16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7108646/
17. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/diy-cloth-face-coverings.html
19. https://makermask.org/the-big-four-criteria-for-community-mask-materials/
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