Why some masking is better than none.

Getty Images/rohprasit

I’m not someone who is a fan of “Do as I say, not as I do.” When I change my behavior, I let you know.

Masking is an area where I get a lot of questions. People often ask me what I’m doing these days. For quite some time, I’ve been wearing an N95 mask in select situations. My choices around masking haven’t changed drastically lately, but they’ve slowly softened over time. I want to explain how I make these decisions—imperfect though they may be— and why I think these choices are scientifically justifiable and ethical.

My current masking practices:

My current practices around masking are as follows:

• I wear an N95 mask whenever I am seeing patients in the hospital. Even if I tested negative the same day, I still wear one to protect my patients and to reduce the odds that I’ll get sick. I’ve gotten a little looser about taking it off when I’m not in a patient area, but I still wear a mask most of the time I’m in the building.

• I wear an N95 mask in high density settings, especially in confined spaces like restrooms and elevators. I was recently at the ID Week conference in Los Angeles, for example. I wore a mask in a lecture hall. (I happened to have my handy portable CO2 monitor in my pocket and noticed the levels were a bit high, so I figured why not?) But when I had coffee with a colleague in a gigantic atrium at the convention center where the ceiling was three stories high, I wasn’t too worried about dropping the mask (my CO2 monitor confirmed those vibes).

• If I am asked to mask, I do it. If I think I am likely to be near high-risk people (e.g., the pharmacy), I mask.

Factors that drive my choices.

There’s no one rubric I follow but here are some principles that guide my decision on when to wear an N95. (Note: masking outdoors is almost entirely pointless, though there are exceptions. I’ve never believed that outdoor masking made sense, and I only did that when it was briefly required in spring of 2020. So, the rest of this applies to indoor settings.)

The main thing to realize is that the risk of getting infected with Covid (or any respiratory virus) is not binary. The risk is tightly linked to the length of exposure and the strength of it. Being in a room with someone who has influenza for 10 minutes is 10 times safer than 100 minutes. And if you’re far from that person, the risk is lower (though not eliminated). So…

• Density/crowd: The more people, the more likely I’ll mask.

• Volume of the space: The amount of airspace in a room matters. This is under-appreciated and many nations actually factored this into their social distancing rules early in the pandemic (i.e., the maximum number of people allowed in a room depended on its volume of 3D space, not its floor space area. Consider two rooms with similar floor space, one with 10 ft ceilings and one with 30 ft ceilings. While it’s more complicated than this, the high-ceiling room should take around three times as long to build up an infectious “dose” of a pathogen like Covid. The mode of transmission and the environment matter greatly.

• How does the air feel: The other day, I was in an indoor space and there were large open windows. At some point, such a setup becomes indistinguishable from being outdoors. (Sometimes I’ll use my handheld CO2 monitor, but nowadays, I mostly go on vibes.) I grant that this can be deceiving, but it’s something I track. If I’m in a room that is stuffy and hot, and people are yapping away, I might grab that mask.

• What are people doing in the room: A loud train station implies lots of talking. A quiet lecture hall implies none. The amount of virus a person puts into a room depends a great deal on what they’re doing. I watch for this.

• Wastewater levels, hospital capacity: Look, if it’s January and there’s a peak where I am, I’m masking more often.

• Other people’s behaviors: If I see a lot of other people masking, I’m more likely to wear one. Why? Partly a social pressure (I’m human). But also, I figure if some people are masking, it’s reasonable to assume that they might be immunocompromised. So, if I see someone wearing a mask near me, I know they are more worried, and I want to help protect them.

Cognitive errors people make about masking.

The major mistake people make in how they think about masking are at the extremes. Some people think masking does not work. They’re wrong. Others think that masking is more effective than it is (especially anything other than a well-fitting N95). For example, trials that showed a 15% reduction in transmission were held up as evidence that masks do not really work that well for Covid. But a 15% reduction in transmission is massive when you think about the effects over many cycles of spread.

Take a virus that has an “R” of 2.3, meaning that each person infects 2.3 other people over 5 days of contagiousness. If that went on for 30 cycles with no other mitigation, you’d have over 330 million cases in 120 days (i.e., the entire US population). But if masks reduced that by 15%, the revised R would be 2. In that case, it would take 150 days for the entire population to be infected. But imagine that a new vaccine could be ready by 120 days into a new outbreak—not impossible! In the masking scenario, only 8 million people would have been infected by day 120! Think how many lives masking would have saved, even though masks “only” reduced transmission by 15%.

The other big error people make is to think in binary terms (as before). We often see anti-maskers complaining that people like me wear a mask for 5 hours on a plane but take it off for 30 minutes, as if that negates the effort. Nope. I’ve reduced my exposure to the virus by 90%. Remember, infections are like doses of medications. You need to get enough to have the effect. It’s not “one droplet in your nose = infection.” So, selective and intermittent masking works.

Ethics and caveats.

One thing driving my thought process is the sad reality that Covid is here to stay. Even if we all stayed home and isolated for a couple of incubation periods and somehow eradicated this pathogen from humans, it is still circulating widely in animals. Animal to human jumps are obviously less common, but they happen enough that this pathogen would be back in circulation among humans relatively quickly. (I had an interesting chat with Dr. Angela Rasmussen about this today; Dr. Rasmussen is a superb scientist who has helped establish that the pandemic almost certainly started in that market in Wuhan.) What that means is that even if we all behaved perfectly, we’re still stuck with this damn virus. That changes the calculation on what we can reasonably expect people to do for the next few years and even decades. We can’t ask people to forsake indoor dining and cocktail parties for the rest of time. In fact, we have to save those “asks” for times when it matters most. That influences the ethics of our choices today. But we can do things to protect those at risk. And that’s why some masking (and testing) remains worth doing, and that is why I still do.

That said…

• None of this is perfect. It’s all harm reduction, and about decreasing risk. If I enter a space in which someone is super-shedding some virus, even dropping my mask for a few minutes to take a few sips of coffee could be enough to get infected. But, in reality, most infections take some time and close exposure, and it might take many hours of exposure to an infected person (or air) to happen. The virus is everywhere, and has been since 2021 or so (in 2020 it was a bit more sporadic). We are constantly being exposed to this thing, and the risk of each exposure is actually pretty low. But the number of opportunities the viruses have is high, so infections add up. The idea is to decrease the amount of virus that’s out there between doses of vaccines and monoclonal antibodies that prevent infections for the immunocompromised.

• One-way masking is very, very effective. I think there’s a sense among some that without 100% masking, everything will fall apart (and has). The reality is that models show that one-way masking is highly effective (assuming a good mask). In fact, I wrote about this back in 2022 (see below). So, for people who are worried about their own safety, wearing a well-fitting N95 mask provides a great deal of protection, even if nobody else in the room is masking.

  When will one-way masking be safe enough for everyone?

Closing thoughts.

This is a work in progress and things can change. But the key for us is to understand that “non-pharmacologic interventions” like masking are neither all-or-none, nor are they purely mathematical. How well NPIs work are a function of both biology and sociology. The exact right thing to do isn’t easy to know, and choices reflect who you are and who you interact with. For me, skipping a crowded event in January sounds great. For others, those types of parties are what make life worth living. Each of us faces a unique situation. My request is not that we each reach the same conclusion, nor that we shame each other for reasonable choices; it’s that we consider these issues with care and do not forget that our decisions do affect the health and well-being of others.

Thanks for reading. I welcome a discussion on this and know this community is respectful and thoughtful. Please do join the conversation.