What is the theory that suggests diseases are caused by bad air from organic decay?

The theory that suggests diseases are caused by "bad air" or miasmas, which are often linked to the decay of organic matter, is known as the Miasma Theory. This historical perspective on disease posited that illnesses were a result of noxious vapors or foul air emanating from decomposing materials or other unsanitary conditions. People believed that inhaling these miasmas led to various health problems, which shaped public health practices for many years.

The Miasma Theory was predominant before the development of more scientifically supported understandings of disease, such as Germ Theory, which attributes disease to specific microorganisms. While Germ Theory eventually replaced Miasma Theory due to advances in microbiology, the concept of miasmas had significant influence on the understanding of disease in earlier times, leading to reforms in sanitation and public health measures based around improving air quality.