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Cause, also known as etiology () and aetiology, is the Causality or origination of something. (2025). 9780781755641, Lippincott Williams & Wilkins. ISBN 9780781755641
The word etiology is derived from the Ancient Greek αἰτιολογία, aitiologia, "giving a reason for" (αἰτία, aitia, "cause"; and -λογία, ). (2025). 9780195219425, Oxford University Press. ISBN 9780195219425
The Ancient Rome scholar Marcus Terentius Varro put forward early ideas about in a 1st-century BC book titled On Agriculture. Varro On Agriculture 1, xii Loeb
Medieval thinking on the etiology of disease showed the influence of Galen and of Hippocrates. Medieval 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 species of the pathogenic bacteria Mycobacterium tuberculosis 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.
In epidemiology, several lines of evidence together are required to for causal inference. Austin Bradford Hill demonstrated a causal relationship between tobacco smoking and lung cancer, and summarized the line of reasoning in the Bradford Hill criteria, a group of nine principles to establish epidemiological causation. This idea of causality was later used in a proposal for a Unified concept of causation.
The term can also refer to a toxin or toxic chemical that causes illness.
Related to this, sometimes several symptoms always appear together, or more often than what could be expected, though it is known that one cannot cause the other. These situations are called , and normally it is assumed that an underlying condition must exist that explains all the symptoms.
Other times there is not a single cause for a disease, but instead a chain of causation from an initial trigger to the development of the clinical disease. An etiological agent of disease may require an independent co-factor, and be subject to a promoter (increases expression) to cause disease. An example of all the above, which was recognized late, is that peptic ulcer disease may be induced by stress, requires the presence of acid secretion in the stomach, and has primary etiology in Helicobacter pylori infection. Many chronic diseases of unknown cause may be studied in this framework to explain multiple epidemiological associations or which may or may not be causally related, and to seek the actual etiology.
Conversely, a single etiology, such as Epstein–Barr virus, may in different circumstances produce different diseases such as mononucleosis, nasopharyngeal carcinoma, or Burkitt's lymphoma.
One example is asthma, which is considered to be a syndrome, consisting of a series of endotypes. This is related to the concept of disease entity.
Other example could be AIDS, where an HIV infection can produce several clinical stages. AIDS is defined as the clinical stage IV of the HIV infection.
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