Etiology (medicine)

Etiology (/iːtiˈɒlədʒi/; alternative spelling aetiology) is the study of causation, or origination.

The word is derived from the Greek αἰτιολογία, aitiologia, "giving a reason for" (αἰτία, aitia, "cause"; and -λογία, ).

In medicine, the term refers to the causes of diseases or pathologies. Where no etiology can be ascertained, the disorder is said to be idiopathic. Traditional accounts of the causes of disease may point to the "evil eye". The Ancient Roman scholar Marcus Terentius Varro put forward early ideas about microorganisms in a 1st-century BC book titled On Agriculture.

Medieval thinking on the etiology of disease showed the influence of Galen and of Hippocrates. Medieval European doctors generally held the view that disease was related to the air and adopted a miasmatic approach to disease etiology.

Etiological discovery in medicine has a history in Robert Koch's demonstration that the tubercle bacillus (Mycobacterium tuberculosis complex) causes the disease tuberculosis, Bacillus anthracis causes anthrax, and Vibrio cholerae causes cholera. This line of thinking and evidence is summarized in Koch's postulates. But proof of causation in infectious diseases is limited to individual cases that provide experimental evidence of etiology.

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