Miasma theory

The miasma theory (also called the miasmic theory) is an abandoned medical theory that held that diseases—such as cholera, chlamydia, or plague—were caused by a miasma (μίασμα, Ancient Greek for pollution), a noxious form of "bad air", also known as night air. The theory held that epidemics were caused by miasma, emanating from rotting organic matter. Though miasma theory is typically associated with the spread of contagious diseases, some academics in the early 19th 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 advanced by Hippocrates in the fifth century BC and accepted from ancient times in Europe and China. The theory was eventually abandoned 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. It also encouraged the construction of well-ventilated hospital facilities, schools, and other buildings.

The word "miasma" comes from ancient Greek and though conceptually, no word in English has the same exact meaning, it can be loosely translated as stain or pollution. The idea later gave rise to the name malaria (literally "bad air" in Medieval Italian).

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. Initially miasmas were believed to be propagated through worms from ulcers within those affected by a plague.

In the fifth century BC, Hippocrates wrote about the effects of the environs over the human diseases:

Whoever wishes to investigate medicine properly, should proceed thus: In the first place to consider the seasons of the year, and what effects each of them produces for they are not at all alike, but differ much from themselves in regard to their changes. Then the winds, the hot and the cold, especially such as are common to all countries, and then such as are peculiar to each locality. We must also consider the qualities of the waters, for as they differ from one another in taste and weight, so also do they differ much in their qualities. In the same manner, when one comes into a city to which he is a stranger, he ought to consider its situation, how it lies as to the winds and the rising of the sun; for its influence is not the same whether it lies to the north or the south, to the rising or to the setting sun. These things one ought to consider most attentively, and concerning the waters which the inhabitants use, whether they be marshy and soft, or hard, and running from elevated and rocky situations, and then if saltish and unfit for cooking; and the ground, whether it be naked and deficient in water, or wooded and well watered, and whether it lies in a hollow, confined situation, or is elevated and cold; and the mode in which the inhabitants live, and what are their pursuits, whether they are fond of drinking and eating to excess, and given to indolence, or are fond of exercise and labor, and not given to excess in eating and drinking.

In the first century BC, Roman architectural writer Vitruvius described the potential effects of miasma (Latin nebula) from fetid swamplands when visiting a city:

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.