In miasma theory, diseases were caused by the presence in the air of a miasma, a poisonous vapour in which were suspended particles of decaying matter that was characterised by its foul smell. The theory originated in the Middle Ages and endured for several centuries. That a killer disease like malaria is so named - from the Italian mala ‘bad’ and aria ‘air’ - is evidence of its suspected miasmic origins.
In 19th-century England the miasma theory made sense to the sanitary reformers. Rapid industrialisation and urbanisation had created many poor, filthy and foul-smelling city neighbourhoods that tended to be the focal points of disease and epidemics. By improving the housing, sanitation and general cleanliness of these existing areas, levels of disease were seen to fall, an observation that lent weight to the theory.
The germ theory of disease emerged in the second half of the 1800s and gradually replaced miasma theory. Although it had been disproved and rejected, the miasma theory’s existence was not without its merits. By removing the causes of bad smells, reformers often inadvertently removed bacteria, the real cause of many diseases.
L Demaitre, 'Air, miasma and contagion - Epidemics in antiquity and the Middle Ages', Bulletin of the History of Medicine, 78/2 (2004), pp 466-468
S Halliday, 'Death and miasma in Victorian London: an obstinate belief', British Medical Journal, 323/7327 (2001), pp 1469-1471
Micro-organisms which can cause disease but have an important role in global ecology.