The miasma theory (also called the miasmatic theory) is an obsolete medical theory that held that diseases—such as cholera, chlamydia, or the Black Death—were caused by a miasma (μίασμα, ancient Greek: "pollution"), a noxious form of "bad air", also known as night air. The theory held that the origin of epidemics was due to a miasma, emanating from rotting organic matter. Though miasma theory is typically associated with the spread of disease, some academics in the early nineteenth century suggested that the theory extended to other conditions as well, e.g. one could become obese by inhaling the odor of food.
The miasma theory was accepted from ancient times in Europe and China. The theory was eventually given up by scientists and physicians after 1880, replaced by the germ theory of disease: specific germs, not miasma, caused specific diseases. However, cultural beliefs about getting rid of odor made the clean-up of waste a high priority for cities.
Miasma was considered to be a poisonous vapor or mist filled with particles from decomposed matter (miasmata) that caused illnesses. The miasmatic position was that diseases were the product of environmental factors such as contaminated water, foul air, and poor hygienic conditions. Such infection was not passed between individuals but would affect individuals within the locale that gave rise to such vapors. It was identifiable by its foul smell. It was also initially believed that miasmas were propagated through worms from ulcers within those affected by a plague.
In India, there was also a miasma theory and the Indians take credit for being the first to put this miasma theory into clinical practice. The Indians invented paan, a gambir paste, that was believed to help prevent miasma; it was considered as the first antimiasmatic application. This gambir tree is found in Southern India and Sri Lanka.
For when the morning breezes blow toward the town at sunrise, if they bring with them mist from marshes and, mingled with the mist, the poisonous breath of creatures of the marshes to be wafted into the bodies of the inhabitants, they will make the site unhealthy.
In the 1850s, miasma was used to explain the spread of cholera in London and in Paris, partly justifying Haussmann's later renovation of the French capital. The disease was said to be preventable by cleansing and scouring of the body and items. Dr. William Farr, the assistant commissioner for the 1851 London census, was an important supporter of the miasma theory. He believed that cholera was transmitted by air, and that there was a deadly concentration of miasmata near the River Thames' banks. Such a belief was in part accepted because of the general lack of air quality in urbanized areas. The wide acceptance of miasma theory during the cholera outbreaks overshadowed the partially correct theory brought forth by John Snow that cholera was spread through water. This slowed the response to the major outbreaks in the Soho district of London and other areas. The Crimean War nurse Florence Nightingale (1820–1910) was a proponent of the theory and worked to make hospitals sanitary and fresh-smelling. It was stated in 'Notes on Nursing for the Labouring Classes' (1860) that Nightingale would "keep the air [the patient] breathes as pure as the external air.
Fear of miasma registered in many early nineteenth century warnings concerning what was termed “unhealthy fog”. The presence of fog strongly indicated the presence of miasma. The miasmas behaved like smoke or mist, blown with air currents, wafted by winds. It did not simply travel on air, it changed the air through which it propagated. The atmosphere was infected by miasma, as diseased people were. Many believed miasma was magical, and was able to change the properties of the air and atmosphere completely.
In China, miasma (Chinese: 瘴氣; pinyin: Zhàngqì; alternate names 瘴毒, 瘴癘) is an old concept of illness, used extensively by ancient Chinese local chronicles and works of literature. Miasma has different names in Chinese culture. Most of the explanations of miasma refer to it as a kind of sickness, or poison gas.
The ancient Chinese thought that miasma was related to the environment of parts of Southern China. The miasma was thought to be caused by the heat, moisture and the dead air in the Southern Chinese mountains. They thought that insects’ waste polluted the air, the fog, water, and the virgin forest harboring a great environment for miasma to occur.
In the descriptions of ancient travelers, soldiers, or local officials (most of them are men of letters) of the phenomenon of miasma, fog, haze, dust, gas, or poison geological gassing were always mentioned. The miasma was thought to have caused a lot of diseases such as the cold, influenza, heat strokes, malaria, or dysentery. In the medical history of China, malaria had been referred to by different names in different dynasty periods. Poisoning and psittacosis were also called miasma in ancient China because they did not accurately understand the cause of disease.
In Sui dynasty, doctor Tsao Yuan-fung mentioned miasma in his book On Pathogen and Syndromes (諸病源候論). He thought that miasma in Southern China is similar with typhoid fever in Northern China. However, in his opinion, miasma is different from malaria and dysentery. In his book, he discussed dysentery in another chapter, and malaria in a single chapter. And he also found that miasma caused different diseases, so he suggested that one should find apt and specific ways to resolve problems.
The knowing of the concept of miasma can be separated into several steps. First, before Western Jin Dynasty, the concept of miasma was gradually forming; at least, in Eastern Han Dynasty, there was no character of miasma. In Eastern Jin, large amounts of northern people moved toward south, miasma was recognized then in the group of men of letters or nobility. After Sui and Tang Dynasty, scholars-bureaucrats traveled and were sent to be the local officials recorded and investigated the miasma. As a result, the government became concerned about the severe cases and the causes of miasma by sending doctors to the area of epidemic to research the disease and heal the patients. In Ming and Qing Dynasties, the edition of the local chronicles record the different miasma in different places.
However, Southern China was highly developed in Ming and Qing Dynasties. The environment changed rapidly, and after the 19th century, western science and medical knowledge were introduced into China, and people knew how to distinguish and deal with the disease. The concept of miasma therefore faded out, due to the progression of medicine in China.
The terrifying miasma diseases in the southern regions of China made it the primary location for relegating officials and sending criminals to exile since the Qin-Han Dynasty. Poet Han Yu (韓愈) of the Tang Dynasty, for example, wrote to his nephew who came to see him off after his banishment to the Chao Prefecture in his poem, En Route (左遷至藍關示姪孫湘):
At dawn I sent a single warning to the throne of the Nine Steps;
At evening I was banished to Chao Yang, eight thousand leagues.
Striving on behalf of a noble dynasty to expel an ignoble government,
How should I, withered and worn, deplore my future lot?
The clouds gather on Ch'in Mountains, I cannot see my home;
The snow bars the passes of Lan, my horse cannot go forward.
But I know that you will come from afar, to fulfil your set purpose,
And lovingly gather my bones, on the banks of that plague-stricken river.
The prevalent belief and predominant fear of the southern region with its "poisonous air and gases" is evident in historical documents.
Similar topics and feelings toward the miasma-infected south are often reflected in early Chinese poetry and records. Most scholars of the time agreed that the geological environments in the south had a direct impact on the population composition and growth. Many historical records reflect that females were less prone to miasma infection, and mortality rates were much higher in the south, especially for the men. This directly influenced agriculture cultivation and the southern economy, as men were the engine of agriculture production. Zhou Qufei (周去非), a local magistrate from the Nan-Sung Dynasty described in his treatise, Representative Answers from the South: "... The men are short and tan, while the women were plump and seldom came down with illness," and exclaimed at the populous female population in the GuangXi region.
This inherent environmental threat also prevented immigration from other regions. Hence, development in the damp and sultry south was much slower than in the north, where the dynasties' political power resided for much of early Chinese history.
Based on “zymotic” theory, people believed vapors called “miasmata” (singular: "miasma") rose from the soil and spread diseases. Miasmata were believed to come from rotting vegetation and foul water—especially in swamps and urban ghettos.
Many people, especially the weak or infirm, avoided breathing night air by going indoors and keeping windows and doors shut. In addition to ideas associated with zymotic theory, there was also a general fear that cold or cool air spread disease. The fear of night air gradually disappeared as understanding about disease increased as well as with improvements in home heating and ventilation. Particularly important was the understanding that the agent spreading malaria was the mosquitoes (active at night) rather than miasmata.
Prior to the late 19th century, night air was considered dangerous in most Western cultures. Throughout the 19th century, the medical community was divided on the explanation for disease proliferation. On one side were the contagionists, believing disease was passed through physical contact, while others believed disease was present in the air in the form of miasma, and thus could proliferate without physical contact. Two members of the latter group were Dr. Thomas S. Smith and Florence Nightingale.
Thomas Southwood Smith spent many years comparing the miasmatic theory to contagionism.
To assume the method of propagation by touch, whether by the person or of infected articles, and to overlook that by the corruption of the air, is at once to increase the real danger, from exposure to noxious effluvia, and to divert attention from the true means of remedy and prevention.
The idea of "contagion", as explaining the spread of disease, appears to have been adopted at a time when, from the neglect of sanitary arrangements, epidemics attacked whole masses of people, and when men had ceased to consider that nature had any laws for her guidance. Beginning with the poets and historians, the word finally made its way into scientific nomenclature, where it has remained ever since [...] a satisfactory explanation for pestilence and an adequate excuse for non-exertion to prevent its recurrence.
The current germ theory accounts for disease proliferation by both direct and indirect physical contact.
In the early nineteenth century, the living conditions of industrialized cities in Britain were increasingly unsanitary. Population was moving in much faster than the infrastructure could support. For example, the population of Manchester doubled within a single decade, leading to overcrowding and a great increase in waste accumulation.  The theory of miasma disease made sense to the sanitary reformers of the mid-19th century. Miasma explained why cholera and other diseases were epidemic in places where the water was undrained and very foul-smelling. As sanitary reform’s engineering leader, London’s Edwin Chadwick, asserted that "all smell is disease", and he proposed that a change in the fundamental structure of sanitation systems was in order to combat increasing urban mortality rates. Chadwick asserted that the problem of epidemics of cholera and typhoid was directly related to urbanization, and he proposed that new, independent sewer systems should be connected to homes. Chadwick supported his proposal with reports from the London Statistical Society which showed dramatic increases in both morbidity and mortality rates since the beginning of urbanization in the early nineteenth century. Though Chadwick proposed reform on the basis of miasma theory, his proposals still contributed to sanitation improvements, such as preventing the reflux of noxious air from sewers back into houses by separate drainage systems in the sanitation designs, which incidentally led to decreased episodes of cholera and thus helped to support the theory.
The miasma theory was consistent with the observations that disease was associated with poor sanitation (and hence foul odours) and that sanitary improvements reduced disease; it was not consistent with the observations of microbiology however which led to the later germ theory of disease. The introduction of medical bacteriology in the 1870s and 1880s provided a challenge to the miasma theory, though consensus was not reached immediately; concerns over sewer gas, which was a major component of the miasma theory developed by Galen and brought to prominence by the Great Stink, led to continuing proponents of the theory who observed that sewers enclosed the refuse of the human bowel, which medical science had discovered could teem with typhoid, cholera, and other microbes.
The work of John Snow is notable for helping to make the connection between cholera and typhoid epidemics and contaminated water sources, which contributed to the eventual demise of miasma theory. During the cholera epidemic of 1854, Snow traced high mortality rates among the citizens of Soho to a water pump in Broad Street. Snow convinced the local government to remove the pump handle, which resulted in a marked decrease in cases of cholera in the area. In 1857, Snow submitted a paper to the British Medical Journal which attributed high numbers of cholera cases to water sources that were contaminated with human waste. Snow used statistical data to show that citizens who received their water from upstream sources were considerably less likely to develop cholera than those who received their water from downstream sources. Though his research supported his hypothesis that contaminated water, not foul air, was the source of cholera epidemics, a review committee concluded that Snow’s findings were not significant enough to warrant change, and they were summarily dismissed. Additionally, other interests intervened in the process of reform. Many water companies and civic authorities pumped water directly from contaminated sources such as the Thames to public wells, and the idea of changing sources or implementing filtration techniques was an unattractive economic prospect. In the face of such economic interests, reform was slow to be adopted.
Even though later disproven by the influence of bacteria and the discovery of viruses, the miasma theory helped make the connection between poor sanitation and disease. This caused public health reforms and encouraged cleanliness, which in Britain led to the legislation of Parliament which approved the Public Health Acts of 1848 and 1858 and the Local Government Act of 1858. The latter of these confers the power of instating investigations into the health and sanitary regulations of any town or place, upon the petition of residents or death rates exceeding the norm. Early medical and sanitary engineering reformers included Henry Austin, Joseph Bazalgette, Edwin Chadwick, Frank Forster, Thomas Hawksley, William Haywood, Henry Letheby, Robert Rawlinson, Sir John Simon and Thomas Wicksteed. These and later British regulatory improvements were reported in the United States as early as 1865.
Particularly notable to nineteenth century sanitation reform is the work of Joseph Bazalgette, chief engineer to London’s Metropolitan Board of Works. Encouraged by the Great Stink, Parliament sanctioned Bazalgette to design and construct a comprehensive system of sewers which intercepted London’s sewage and diverted it away from its water supply. The system helped purify London’s water supply and saved the city from epidemics. In 1866, the last of the three great British cholera epidemics took hold in a small area of Whitechapel. However, the area was not yet connected to Bazalgette’s system, and the confined area of the epidemic in London acted as testament to the efficiency of the system’s design.
London was the first city to create a complex civic administration which could coordinate modern urban services, from public transport to housing, clean water to education. London's County Council was acknowledged as the most progressive metropolitan government in the world. Fifty years earlier, London had been the worst slum city of the industrialized world: over-crowded, congested, polluted and ridden with disease...
The miasma theory did contribute to containing disease in urban settlements, but did not allow for a suitable approach to safe excreta reuse in agriculture to be adopted. It was one of the causes for abandoning the prevailing practice of collecting human excreta from urban settlements and reusing them in the surrounding farmland (nowadays referred to as the ecosan approach of "closing the loop" when done in a safe manner). Such resource recovery schemes were common in many European cities until the 19th century before the arrival of sewer-based sanitation systems.
Throughout the nineteenth century public health, sanitation and the influence of miasma became the main reasons for the controversial practice of cremation. The miasma theory stated that infectious diseases were spread by noxious gases emitted from decaying organic matter, which included decaying corpses. This public health argument for cremation faded along with the miasma theory.
Although the connection between germ and disease was proposed quite early, it was not until the late-1800s that the germ theory was generally accepted. The miasmatic theory was challenged by John Snow, suggesting that there was some means by which the disease was spread via a poison or morbid material (orig: materies morbi) in the water. He suggested this before and in response to an epidemic on Broad Street in central London in 1854. Because of the miasmatic theory's predominance among Italian scientists, the discovery in the same year by Filippo Pacini of the bacillus that caused the disease was completely ignored.
In 1846, the Nuisances Removal and Diseases Prevention Act was passed to identify whether the transmission of Cholera is by air or by water. The bill was used to encourage the owner to clean their dwelling and connect them to sewers.
Some years later in 1855, John Snow made a testimony against the Amendment to this bill that regularized air pollution of some industries. He claimed that:
That is possible; but I believe that the poison of the cholera is either swallowed in water, or got directly from some other person in the family, or in the room; I believe it is quite an exception for it to be conveyed in the air; though if the matter gets dry it may be wafted a short distance.
At the same year, William Farr, who was then the major supporter of the Miasma Theory, issued a report to criticize the germ theory. Farr and the Committee wrote that:
After careful inquiry, we see no reason to adopt this belief. We do not feel it established that the water was contaminated in the manner alleged; nor is there before us any sufficient evidence to show whether inhabitants of that district, drinking from that well, suffered in proportion more than other inhabitants of the district who drank from other sources.
The more formal experiments on the relationship between germ and disease were conducted by Louis Pasteur between 1860 and 1864. He discovered the pathology of the puerperal fever and the pyogenic vibrio in the blood, and suggested using boric acid to kill these microorganisms before and after confinement.
By 1866, eight years after the death of John Snow, William Farr publicly acknowledged that the miasma theory on the transmission of cholera was wrong, by his statistical justification on the death rate.