The messaging on masks has been very confusing.  For several weeks, the CDC said the public doesn’t need masks, then finally, the surgeon general was demonstrating how to make a mask out of a T-shirt. I’m convinced that the CDC was so slow to recommend masks simply because they have been so hard to come by.  But the delay in recommending masks has caused a lot of confusion. 

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Section added 2/22/21: Masks have produced a lot of controversy, but I am a big fan of mask wearing indoors. This does several things, it usually prevents infection if you’re wearing an N95 or KN95. However, studies suggest that even if you get infected, a masks will help you have a lower initial viral load on exposure, greatly reducing your symptoms! I personally always wear a mask indoors, and I rarely eat indoors right now.

Outdoors are a different story. Unless you are in a tightly clustered large group of people, you probably do not need to wear a mask outdoors! Some municipalities encourage or require mask wearing outside, but this is usually unnecessary. I am not saying you should ignore local requirements! I’m just saying that when you are going for a walk, a hike or a bike ride, a mask is not necessary.
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First, let’s talk about the words you’re hearing now!

Cloth Face Covering: A “cloth face covering” (I’ll say CFC for short here) is not technically a mask as the CDC defines it, and is not considering Personal Protective Equipment (PPE) from a medical perspective.  This a t-shirt, bandana, buff, or anything else that can be used to cover your nose and mouth.  The virus can still get both into your nose or mouth, or leave your body through these coverings, but it’s much better than nothing.  A lot of people who are trying to be responsible, but can’t find a mask to buy, are using these coverings.  If you hear someone saying they don’t work, they mean that they aren’t completely effective, but they are much better than nothing! Even if you sneeze, a face covering will capture larger droplets, slow the velocity of the sneeze, and help protect those around you.  If all you have is a CFC, you should still wear it when you go out!

According to Fischer et al, gator style masks may be even worse than wearing nothing at all, since they may break up droplets into a smaller size that stays in the atmosphere longer! So avoid a neck-gator style mask!

Face mask: A “face mask” is a filtering mask that covers the nose and mouth, but does not seal around the nose and mouth.  This includes the blue surgical mask that you see a lot of today.  These masks are designed to prevent material from medical worker’s  face and nose from getting to a patient during a procedure, while still allowing somewhat normal breathing.  They filter incoming air to some degree, but there are large gaps at the sides of the mask, so there are not very effective at preventing infection by SARS-2.  Coughing, sneezing and singing will still expel air from the sides while wearing these masks!  They aren’t completely effective, but they are certainly better than nothing, and will prevent transmission through simple talking. If you have one, please wear it!

UPDATE: Now that KN95 masks and some N95s are available (see below), I can no longer recommend wearing these masks.

Respirator: These masks seal against the sides of the face cover at least the nose and mouth.  They are designed to filter the air and prevent particles from entering the nose and mouth.  N95s prevent 95% of viruses from getting through and are the preferred mask for medical workers in most situations right now.  Unfortunately, they have been in very short supply since the beginning of the pandemic, so the public is being asked not to purchase these for now.  Doctors tells me that N95s are not adequate protection while performing certain procedures on COVID patients!  One told me a story about 14 medical workers being infected by a single patient during a procedure!  This work requires a Powered Air-Purifying Respirator (PAPR).  These masks cover the entire face and also blow air into the mask, pushing virus out.

If you have an N95 with a valve in the front, these masks will still vent air when you cough or sneeze, so be aware that it will not protect others from virus coming from you! N95s with no valve are the best choice for protecting both you and those around you. Again, hold off on purchasing these until there are in greater abundance.

I see a lot of very nice looking fitted masks with a little round filter in the front.  These filter out large particles like dust or large droplets, but not necessarily small virus particles.  While much better than nothing, these are not necessarily N95 masks! Read the product information carefully when buying these masks.

KN95 Masks: A new style of mask is being sold in the US now, labeled KN95. These masks are made in China and designed to filter out 95% of viral particles, like N95s. However, they are certified by a Chinese agency, and not by the FDA or CDC. They have been allowed to be sold in the US on an emergency basis. Users say they fit more loosely than N95 masks.

There are lots of studies showing the effectiveness of these masks, and unfortunately I don’t have one ultimate study to share with you.  Suay, a clothing company in LA, did a study suggesting that normal blue shop towels (like Tool Box Shop Towels or Zep Industrial Towels) do a much better job at filtering than cotton, and are a cheap and available alternative to an N95 when sewn into a mask. My sister-in-law Penny is part of a team that makes masks for the local hospitals in Bozeman.  These are homemade masks with a pocket for a HEPA filter. She’s sending me some, and I’m going to add a Shop Towel to mine! Both designs are posted below.

Here’s a few tips for wearing your mask:

1. Your CFC or mask must cover your mouth and nose.  Leaving your nose hanging out, or simply wearing it as a chin mask is not adequate! 
2. When adjusting your mask assume both your hands and the mask are contaminated.  Wash your hands before AND after adjusting.
3. 30 min of UV light effectively kills SARS-2 virus.  In the bright sunlight, it may only take a few minutes.  I sterilize my mask by leaving it in the sun for a half hour after a shopping trip.  If you have a cloth face covering or mask, machine washing is a better choice.

In addition to preventing infection, masks appear to reduce the viral load in newly infected patients, leading to less severe symptoms! So even if you get infected while wearing a mask, your symptoms are likely to be less severe!

As we think about re-opening the economy, face coverings, even the bandana type, will really help keep new infections low.  So wear a mask when you go out in public! Any improvements will hasten the day when businesses can re-open. I am awaiting data to see what the infection rate is at businesses in which employees wear masks. Hopefully, this data will come out soon.

Don’t fear, but be smart!
Erik

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Update, February 23rd, 2023,

Cochrane Report on the Effectiveness of Masks:  Jefferson et al released a meta-study through Cochrane Reviews on the effectiveness of medical masks (surgical masks) and medical respirators (N95) in public settings.  A meta-study is a study in which the authors gather information from published articles and try to draw conclusions from a large body of data. They do not gather a new set of data.

The Jefferson et al study reviewed 78 different studies, including data from pre-COVID flu outbreaks.  Their conclusions are sobering.  First, the authors suggest that there is virtually no benefit to wearing a medical surgical mask over not wearing a mask in most settings.  If you’ve been reading my blog for long, you will know that this conclusion does not surprise me.  Blue surgical masks have large gaps in the sides and do not filter air leaving the mouth and nose.  They were designed to prevent droplets from a medical worker from contacting a patient, not to prevent transmission of aerosol based agents.  This is a problem, since most mask wearing people in public during the pandemic were wearing surgical masks.  These people thought they were protected from aerosols, but they were not.

The study also concludes, however, that N95 masks didn’t perform much better.  In fact, for lab tested COVID, the difference was statistically insignificant, meaning that the difference between wearing N95s or surgical masks was so small, it could not be proven to be a real difference statistically. 

I have to point out that the Jefferson meta-study points out that many of the studies they reviewed had various failings that may have made them unreliable.  Much of the data was collected through self-reporting of participants, which is a source of inaccuracy, and participants were often non-random, making application to the general population difficult.  So some of the conclusions may have suffered from these kinds of errors.

As you know, I’ve been a proponent of wearing N95, KN95, or KF94 masks when indoors during the pandemic.  Unfortunately, N95s are tight and intolerable for most people for long periods, so most people didn’t want to wear them at all.  Those that did were not careful to make sure the mask fits properly, making the mask ineffective.  This is part of the reason I wore a KF94 (Korean) during the later stages of the pandemic when I had choices.

So have I been wrong this whole time?  Well, yes and no.  I wore a KN95 in all kinds of environments while traveling during the pandemic.  When I finally got COVID in January of 2021, I was not wearing my mask, working in a “gray area” environment with people that I later found out had COVID.  I was technically indoors, but the room had a lot of ventilation, so I thought I would be OK. Obviously, I was incorrect.  All this to say, I think my KN95 was effective for much of the pandemic.  On the other hand, I am a scientist in the infectious disease field, and have had a lot of experience wearing and fitting these masks to myself, so I am not a typical user.  It may certainly be that my experience does not translate to non-scientists.

If you still have not had COVID and are not high risk, I might say that the current version has an extremely low fatality rate, and it may now be worth the risk to say good-bye to the mask.  I know the large majority of you have done this already.

If you are at high risk, I still think an N95, KN95, or KF94 can be effective for you.  In order for it to be effective, however, you need to make sure it is properly fitted, making sure you don’t have gaps between your nose and cheek.  The mask should filter the air coming into your nose and mouth.

Since I had COVID last January, I no longer wear a KN94, and enjoy eating indoors in restaurants again.  I’ve basically been back to normal for a long time.

Dr. Visay Prasad has an excellent video describing some of the details of the meta-study.  He is an epidemiologist from UCSF. 
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CDC report on filtration.

Masks effective in protecting healthcare workers, Bartoszko et al.

Study on the best masks, Fisher et al.

Mask may reduce symptoms and even provide some immunity, Ghandi et al.