Miasma theory

Obsolete medical theory about the transmission of disease through bad air

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, the breath of humans and animals, and other odors. The theory explained why epidemics tend to happen in places with high population density, such as cities, as well as in swampy or hot and humid climates; and it addressed correlations between contagious diseases and lacking hygiene, lack of fresh air, and contacting the sick.

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