The Washington PostDemocracy Dies in Darkness

Revisiting a 19th century medical idea could help address covid-19

When germ theory displaced the idea of “miasmas” we lost important knowledge about tackling airborne disease.

Pedestrians wearing protective masks walk past diners eating outdoors in Brooklyn's Park Slope neighborhood last month. (Amir Hamja/Bloomberg)

Face masks. Ventilation. Air purifiers. Social distancing. Breathing has been in the news and on our minds for the past year, since the evidence became increasingly clear that the coronavirus spreads via aerosols, infectious viral particles suspended in the air. In everyday language, the coronavirus is airborne.

To protect our health, we have begun to pay attention to the air we breathe, much as people did in the 19th century, when they believed that airborne “miasmas” — vapors and gases released by decomposition — spread disease. After scientists learned more about human respiration in the late 18th and early 19th centuries, they added “vitiated air,” meaning air that had been exhaled and corrupted by someone’s body, to miasmas as likely health threats. Today’s research into how coronavirus has spread through aerosol droplets closely mirrors 19th century discussions of vitiated air.

Revisiting the history of miasma theory and its subsequent disappearance from our understandings of disease tells us that our routines for disease prevention have fluctuated with changing knowledge about disease causation. Some of these fluctuations have been beneficial, such as washing hands to reduce bacterial spread and installing window screens to diminish contact with mosquitoes.

Yet other fluctuations, such as ignoring earlier prescriptions for how to combat aerial health threats, have contributed to our current health crisis and pitched political debates over interventions. By recovering the everyday routines that Americans used to combat aerial health threats in the 19th century, we can normalize the seemingly new advice of aerosol engineers and disease experts.

In the early 19th century, medical knowledge was a fusion of ancient concepts and recent observations that explained how illnesses spread. Today we think of diseases as having specific, identifiable causes and symptoms, but in the early 19th century, people experienced illness as a set of interactions between their bodies and the world around them. Medical experts believed that a range of fevers were caused by changes in the ambient environment and that a few specific diseases, like smallpox, somehow spread from person to person.

To protect people’s health from these aerial threats, disease prevention under miasma theory included a range of practices aimed at protecting and improving the air that people breathed. These practices emphasized ample fresh air and sunshine as natural disinfectants necessary for good health.

People also tried to avoid miasmas by not living near or lingering in swamps and marshes, where masses of decomposing organic matter released potent miasmas. (We now know that mosquitoes were the real threat.) They also were wary of crowded churches and theaters, where they might catch various fevers called “crowd diseases” by inhaling vitiated air. In their homes, women opened windows to “air out” rooms and adopted ventilation techniques to create a constant flow of fresh air, meaning air that had not already been exhaled. Women were especially vigilant about the air of sickrooms, the name for any room in which an ill family member convalesced; they developed methods to purify the air of sickrooms and direct it out of the house, away from other family members.

To avoid inhaling foul airs while moving through the city, individuals covered their noses with perfumed handkerchiefs or buried noses in fragrant nosegays — both rudimentary versions of the masks we’ve adopted during the coronavirus pandemic. By the 1870s, scientists were developing face masks that would filter air through charcoal particles, and public health authorities started monitoring the patterns of air movement, paying attention to any smoke- and stench-spewing factories that might be upwind of their jurisdictions. Miasma theory raised concerns about stenches from new and bigger industries such as oil refining and meat packing, concerns that new urban public health departments tried to address through regulation. Because expanding cities created crowded living and working conditions, avoiding miasmas and vitiated air increasingly required government intervention.

Germ theory emerged in the 1870s and 1880s from scientists’ experiments to determine exactly how illnesses spread. Through their work in laboratories, rather than observations of the sickroom, French chemist Louis Pasteur and German physician Robert Koch demonstrated that microbes were linked to the deadliest diseases. Scientists in the 1880s used Pasteur’s and Koch’s experimental methods to rapidly identify the bacteria that caused specific illnesses, solidifying germ theory with scientific evidence.

Routines for disease prevention shifted as germ theory taught people to worry about microscopic bacteria and viruses rather than ill-defined miasmas. Household health guides and women’s magazines emphasized behaviors such as washing one’s hands with soap and water or sanitizing surfaces as the best way to fight germs.

Governments initially protected public health through city services such as water purification, sewerage and garbage removal and also added an increasing number of vaccines in the 20th century. These disease-prevention techniques became a routine part of daily life in the 20th century, replacing the aerial practices used by previous generations. Fresh air, which had been central to health under miasma theory but increasingly required industrial regulation in crowded cities, was transformed into an aesthetic preference.

Today, research into covid-19 has revealed that the novel coronavirus spreads through the air rather than via surfaces — a discovery that has led many to criticize “sanitation or hygiene theater” and over-cleaning as the wrong response. However, the impulse to sanitize and deep-clean everything is the result of over a century of following germ theory, which emphasized cleaning and disinfecting all surfaces to combat germs. We have also learned to see surface sanitation in sparkling surfaces, which means that businesses and schools eager to reopen can demonstrate cleanliness in a way that they can’t show air control; fresh and vitiated air looks the same. (This may be changing as expensive ventilation devices enter the market).

Considering this history is key to understanding — rather than lampooning — why people have tried to apply their received knowledge on how to protect health during an unprecedented crisis. It also points to one problem that fueled the spread of covid-19: Our society neglected and forgot aerial health practices when germ theory promised better disease control.

Covid-19, however, has revealed that simply relying on surface sanitation and vaccines to protect our health is insufficient. Bringing back a modern version of the practices of the 19th century also has major benefits. Wearing masks and social distancing have contributed to the mildest flu season in recent history. Better ventilated buildings and large, outdoor spaces allow people to gather without inhaling each other’s vitiated air or aerosol droplets. Health practices don’t need to be an either/or. Adding these tactics to our germ-killing habits of handwashing and surface sanitation will better prepare society and culture to encounter the viruses to come. Fresh air remains good for our health.