János Hugo Bruno "Hans" Selye CC (/ˈsɛljeɪ/[dubious – discuss]; Hungarian: Selye János Hungarian pronunciation: [ˈʃɛjɛ]; January 26, 1907 – October 16, 1982) was a pioneering Hungarian-Canadian endocrinologist who conducted important scientific work on the hypothetical non-specific response of an organism to stressors.

Selye was born in Vienna, Austria-Hungary on January 26, 1907, and grew up in Komárom (the town with Hungarian majority in present-day Slovakia was cut by the Treaty of Trianon in 1920).

After completing his medical degree and a doctorate degree in organic chemistry at the German University of Prague, he received a Rockefeller Foundation fellowship to study (1931) at Johns Hopkins in Baltimore[5] and later moved to the Department of Biochemistry at McGill University in Montreal in 1932[6] where he studied under the sponsorship of James Bertram Collip (1892–1965).

(A stressor is a chemical or biological agent, environmental condition, external stimulus or an event seen as causing stress to an organism.)

[8] Working with doctoral student Thomas McKeown (1912–1988), Selye published a report that used the word "stress" to describe these responses to adverse events.

He at first believed that he had discovered a new hormone, but was proved wrong when every irritating substance he injected produced the same symptoms (swelling of the adrenal cortex, atrophy of the thymus, gastric and duodenal ulcers).

[10] This, paired with his observation that people with different diseases exhibit similar symptoms, led to his description of the effects of "noxious agents" as he at first called it.

Selye acknowledged the influence of Claude Bernard (1813–1878), who developed the idea of milieu intérieur, and of the "homeostasis" of Walter Cannon (1871–1945).

While Selye's work attracted continued support from advocates of psychosomatic medicine, many in experimental physiology concluded that his concepts were too vague and unmeasurable.

Later, New York attorney Edwin Jacob contacted Selye as he prepared a defense against liability actions brought against tobacco companies.

One lawyer advised him to "comment on the unlikelihood of there being a mechanism by which smoking could cause cardiovascular disease” and to emphasize the "stressful" effect that anti-smoking messages had on the US population.