A Brief History of Masks

Created/Modified: 2025-11-10/2025-11-11

Engineering is the primary profession that protects public health, with medicine providing an important backstop in the form of vaccination when engineering measures either fail, or physicians and others prevent them from being implemented.

Engineers--not physicians--keep your water free from disease and treat your sewage before it is released into the wild. Engineers ensure the public buildings you inhabit have more-or-less adequate ventilation to supply air for breathing most of the time, although we have recently discovered that old standards were not really adequate to do that, much less ensure the air available for breathing is--like the water you drink--mostly free from disease.

When water treatment plants fail, boil water advisories are issued and every individual becomes responsible for their own health and safety, which always--always--results in more disease than when engineering measures are in place and working properly.

In the absence of upgraded air handling facilities that conform to ASHRAE standard 241 for infection control, public indoor public spaces--especially hospitals and schools, but all public buildings, offices, churches, law courts, and so on--are seas of floating respiratory aerosols, which are fine particles that carry pretty much anything that was once in your body out of your body and into the air.

Aerosols are copiously produced by such rare and usual acts as breathing, talking, singing, talking loudly, and more. A group of non-scientists once got together and imagined that there were just a few medical procedures that generated a significant aerosol load, and without actually measuring any aerosols produced by anything they declared that these things they had imagined to be "AGPs" [aerosol generating procedures] were the only things anyone had to worry about.

They were wrong, which should come as no surprise to anyone: what we imagine and what actually exists is if anything slightly anti-correlated in most cases. The more likely things seem to our monkey imaginations the less likely they are to happen in the cold and careless reality we inhabit.

So aerosols are:

• produced all the time by humans simply breathing and talking
• hang in the air like cigarette smoke for tens of minutes or even hours
• can travel over very long distances, through unfiltered ventilation shafts, around corners, up stairways, down hallways, and anywhere air is apt to get
• are capable of carrying pretty much anything that was inside our body along with them.

It follows from this that aerosols are capable of spreading disease.

In fact, a moment's thought regarding the necessity of evolution tells us that any disease that is capable of being spread by large droplets that come out of our mouths, like spit or sputum, will also almost certainly be spread by respiratory aerosols that come out of our mouths as we breathe and talk.

Consider: evolution works because individuals that make more (imperfect) copies of themselves necessarily come to outnumber organisms of the same kind that make fewer imperfect copies of themselves. This is a tautology. Furthermore, some of those imperfect copies are more capable of reproducing themselves in the conditions they find themselves in than others. That is: the imperfect copying mechanism of DNA or (for some viruses) RNA replication results in some members of the next generation having an advantage over the others. Those ones will make more copies of themselves. This happens in every generation, with the copies that do best--as a matter of simple mathematical necessity--dominating future populations.

So consider a virus that spreads well in large droplets that quickly fall to the ground. There is no sharp cutoff where this happens, because air currents, temperature, humidity, and so on, make a difference, but smaller droplets fall more slowly, so a softer upward air current is capable of keeping them aloft indefinitely, wafting them around the room, out the door, and down the hallway. By the time we're down to a few dozen microns, long-lived droplets are becoming pretty common, and they just get more common as the size goes down from there.

It is also a matter of mathematical necessity that a virus that is only good at spreading in large droplets that don't usually get wafted long distances will not have as many chances to find a new host as one that can also spread via aerosols that can stay in the air for minutes rather than fractions of a second and travel tens of meters rather than a few feet.

This kind of situation, where one way of being gives a reproductive advantage, is called "selective pressure", although it's not pressure: it's just numbers. If it is physically possible for a virus to retain its integrity inside an aerosol particle, it will have better odds of being inhaled and given a chance to infect someone else. Eventually, almost all droplet-spread viruses will be the offspring of ones that could also spread by aerosols.

Anything else requires turning off evolution in this case, and no one has ever tried to explain how that could happen.

Personally, I don't think it does.

So we should always assume that any virus can be spread via aerosols. Bacteria, too. I know personally of at least one case of E. coli infection due to aerosol spread.

As such, we should expect anti-aerosol technology to do better at protecting people from viruses than anything else. And we have such technology in hand.

N95 respirators and similar--KN95s, N100s, and so on--are effective at preventing inhalation of fine particulate matter in the air. They are used throughout industry to protect workers from a wide range of inhalation hazards, from asbestos to smoke to fungal spores to... bio-aerosols.

These are devices that work via well-understood physical principles to both mechanically filter large particles (where "large" means "microns") and electro-statically filter small particles. Electrostatic filtering works by including a layer in the masks that have polarized molecules on their surface, so passing particles feel the resulting electric field and get pulled in and stuck even though the holes in the mask are larger than the particles.

This is sometimes called "electret filtering" and it's a commonplace that everyone who has ever asked anything about N95 masks has had explained to them, often many times, but because people lie, you will still find individuals who pretend not to know what I've just described, so they will lie that they have never been told this and don't know about it, and go on to ask or assert, "So how does a mask [that I've been told many times traps particles smaller than the holes in it using electrostatics] trap particles smaller than the holes in it?"

The important thing in responding to these people is to not go along with their lie, the pretense that they've never heard about how electret filtering works. Instead, ask they why they are lying to you that they've never heard of it before. Ask them if they're too stupid to understand the explanation, or if they're just dishonest. Maybe remind them that some moral codes say lying--often called "bearing false witness"--is a bad thing. Try it. It'll be fun.

So we know N95s and similar work when properly fitted, and we know they have been used uncontroversially for decades across a dizzying array of industries to keep workers safe on industrial sites and in laboratories.

But not in hospitals and other health care venues, except for those cases where a group of non-scientists imagined they were dealing with "aerosol generating procedures". In health care there has been an anti-mask resistance going back a full century.

I'm reading The Great Influenza: The Story of the Deadliest Plague in History by John M. Barry, which is a history of the 1918 flu in the US. The book describes a litany of medical and military and political failure from start to finish, with physicians--who are trained to be reactive and cautious--repeatedly failing to do anything useful to prevent the spread of this deadly flu variant.

This passage caught my eye, describing a meeting where Joseph Capps, MD, gave a presentation to a group that included William Welch, MD, the most politically powerful voice in US medicine for decades:

"Then he [Capps] demonstrated for them an innovation he had experimented with: the wearing of gauze masks by patients with respiratory disease."

Capps later wrote a paper for the Journal of the (US) American Medical Association, which was published on August 10, 1918. In it he describes the success he has had with gauze masks, and mentions an earlier paper by Weaver that inspired his work, and a follow-up coming from his superior, Major Haller--this was wartime, and these were all physicians who had joined the army--that would describe the efficacy of various gauze type and layer thicknesses.

The data from these studies was extremely interesting, and the effects were dramatic enough that Capps had actually stopped experimenting after just three weeks and mandated a comprehensive masking protocol, resulting in what appeared to be a significant drop in the rate of "cross-infection" between patients and staff, and patients and patients.

The followup to all of this was, as near as I can tell, a mix of studious ignorance and carefully crafted push-back. A subsequent paper by W. H. Kellog, the Secretary and Executive of the California State Board of Health, and Grace MacMillan--the scientist who actually did the work-- claimed that badly implemented mask mandates that ignored the known possibility of aerosol spread had no effect on population-level pandemic dynamics.

This dance was to be repeated for the next one hundred years, while engineers and physicists ramped up respirator technology to protect workers in every industry except health care, and physicians continued to run poorly designed studies that only demonstrated they didn't understand fluid mechanics or the theory of evolution.

Every competently conducted engineering study on N95s has shown they offer superior protection against dangerous aerosols. For example a study from 2012 found:

A new laboratory study supports the long-debated view that airborne viruses play a role in spreading influenza and that N95 respirators provide the best protection against airborne viruses, with surgical masks affording much less.

A US-Chinese team of researchers created a simulated examination room with mechanized mannequins spaced 6 feet apart to represent coughing and breathing humans. They found that flu viruses floated between the two and were "inhaled" by the breathing mannequin, but that an N95 respirator sealed to the mannequin's face stopped 99.8% of them.

A poorly fitted respirator or a loose-fitting surgical mask, by contrast, blocked only about two thirds of the virus particles.

The researchers say their findings suggest that "anyone present in a room with a patient who has influenza might be at risk of exposure" and that properly fitted N95 respirators provide maximal protection. Their report is an early online publication in Clinical Infectious Diseases.

Current guidance from the US Centers for Disease Control and Prevention (CDC) says that flu viruses spread primarily via virus-laden large droplets from coughs and sneezes, but that these generally travel in the air only about 3 feet.

As noted in an editorial accompanying the new study, the role of smaller aerosol particles that travel farther is uncertain and controversial, which has engendered confusion about the best infection control measures for healthcare workers.

The only thing "controversial" about aerosol spread of flu, covid, and other diseases is how health care professionals who know nothing about fluid mechanics--or, apparently, evolution--have managed to sow doubt about it for a full century. THAT should be not just controversial, but scandalous. Physicians are not trained in fluid mechanics, which is an extremely dense and difficult area of physics and engineering, and without that training and the experimental and computational explorations that go along with it, there is negligible possibility of being able to reason effectively about the subject.

Unfortunately, this inability to reason about fluid mechanics contaminates practically every study of N95s in health care carried out by physicians, such as this one that ran in the decade before covid. The study description says, comparing N95s with medical masks (MMs):

Participants will be instructed to don a new N95/MM with each patient interaction, every time a participant encounter occurs within 6 feet of a patient who has suspected or confirmed respiratory infection. [emphasis added]

If Gabriel Garcia Marquez wrote a novella about this study he'd call it A Chronicle of a Conclusion Foretold:

Among outpatient HCP [health care personnel], N95 respirators vs medical masks as worn by participants in this trial resulted in no significant difference in the incidence of laboratory-confirmed influenza." [emphasis added]

As is so often the case, The Vertlantic said it best:

This kind of "non-inferiority" study has been repeated with covid rather than flu as the target and was just as badly mangled by physicians who have no understanding of fluid mechanics.

It should be the default assumption of any study of respirators that all diseases are spread by aerosols, both because the evolutionary argument tells us that that is overwhelmingly plausible and because we know that every time anyone has gone looking for aerosol spread they have found it.

Anything else at this point in our understanding is somewhere between gross incompetence and scientific fraud.

Masking works to a degree even with medical masks when applied as rigorously as Capps did it. That followup studies didn't implement and enforce the same disciplines he was easily able to is laxity on the investigator's part, perhaps driven by a desire to not have science dictate their behaviour.

Today, N95s are enormously superior to medical masks, in part because they depend on the well-understood, well-known physics of electret filtering that absolutely everyone who has ever asked anything about N95s has by now had explained to them many, many times.

The failure of "health care professionals" to update their beliefs about how most disease spreads puts them in the same camp as Creationists when it comes to evolution denial, and far beyond that when it comes to denial of basic physical laws as embodied in engineering practice.

The Canadian Standards Association has published a new draft standard, “Selection, Use, and Care of Respirators” (CSA Z94.4:25) that gives health care workers and their clients the same level of N95 protection we routinely afford to workers in every other industry where airborne particulates pose a danger to human well-being. The standard specifies that:

By default the use of respirators by health-care providers throughout the health-care facility is required unless a detailed risk assessment by qualified experts deems a space exempt due to engineered risk reduction (such as displacement ventilation, upper air germicidal ultraviolet radiation, etc.).

There are a large number of straightforward engineering upgrades to hospital and clinic ventilation and filtration systems that will dramatically reduce the need for universal N95 wear among health care workers. Those upgrades will save money by lowering absenteeism and improve the quality of patient care.

So a standards-driven N95 mandate would be short-lived, if we let engineers take over responsibility for clean air in precisely the same way we have allowed them to take over responsibility for clean water, where they have kept people largely safe from water-borne disease for almost a hundred and fifty years.

Just why would we not do that?