The term “stress” entered scientific literature in July 1936, when Hungarian-Canadian endocrinologist Hans Selye published a 74-line letter in the journal Nature. The piece, titled “A Syndrome Produced by Diverse Nocuous Agents,” described a universal pattern of bodily responses that occurred regardless of what was harming an organism. That short publication launched a concept that would reshape medicine, psychology, and everyday language over the next nine decades.
What Selye Actually Described in 1936
Selye didn’t set out to study stress. He was a young researcher at McGill University experimenting on rats, exposing them to various harmful conditions: cold, injury, toxic substances, excessive exercise. What struck him was that no matter what he did to the animals, their bodies reacted with the same general pattern. The adrenal glands enlarged, immune tissue shrank, and the stomach lining developed ulcers.
He called this the General Adaptation Syndrome, a three-stage process the body goes through when facing any sustained threat. First comes an alarm reaction, where the body mobilizes its defenses. Then a stage of resistance, where the body appears to cope. Finally, if the harmful exposure continues long enough, a stage of exhaustion sets in and the body’s defenses break down. The word “stress” was Selye’s shorthand for the biological state driving this entire sequence. Notably, his original manuscript used the word “noxious” to describe the harmful agents, but a Nature editor changed it to the less common “nocuous” before publication.
The Ideas That Came Before Selye
Selye didn’t work in a vacuum. Two earlier scientists laid critical groundwork. In the mid-1800s, French physiologist Claude Bernard proposed that the body maintains a stable internal environment, and that disruptions to this stability could cause disease. American physiologist Walter Cannon built on Bernard’s ideas in the early twentieth century, describing in 1915 how the body prepares to confront or flee danger. Cannon coined the phrase “fight or flight” and, in 1932, introduced the term “homeostasis” to describe the body’s ability to keep its internal conditions steady despite external challenges.
Cannon’s work bridged biology and psychology, showing that emotional states like fear and rage triggered measurable physical changes: a racing heart, surging adrenaline, redirected blood flow. But Cannon never grouped all of these responses under a single unifying label the way Selye did. It was Selye who packaged the concept into a framework broad enough to apply across medicine, and who gave it the name that stuck.
How “Stress” Spread Across Disciplines
During the middle decades of the twentieth century, Selye’s concept of biological stress was adopted and adapted by researchers in fields far beyond endocrinology. Military medicine used it to understand combat fatigue. Veterinary medicine applied it to animal welfare. Psychiatrists, allergists, population scientists, and sociobiologists all found the framework useful for explaining how sustained pressure on a living system eventually produces breakdown.
A crucial shift happened as the concept migrated into psychology. Selye originally described stress as a purely physical phenomenon: hormones, organ changes, measurable tissue damage. But by mid-century, scientists and Western societies began labeling the combination of physiological and psychological responses people display when things feel overwhelming and out of balance as “stress.” The modern definition reflects this merger. As one widely cited formulation puts it, stress is a pattern of physiological, behavioral, emotional, and cognitive responses to real or imagined stimuli that are perceived as blocking a goal or threatening well-being. The inseparable combination of body and mind is what makes the concept so powerful, and so hard to pin down precisely.
Why the Word Itself Caused Problems
The very success of “stress” as a term created lasting confusion. In everyday English, “stress” can refer to the thing causing pressure (a deadline, a divorce), the body’s response to that pressure, or the subjective feeling of being overwhelmed. Scientists struggled with the same ambiguity. Is stress what happens to you, or what happens inside you? Is all stress harmful, or can some be beneficial?
Selye later tried to address this by distinguishing between “eustress” (positive, motivating pressure) and “distress” (harmful, depleting pressure). The distinction never fully caught on in either scientific or popular usage. People kept using the single word “stress” to mean all of it, and researchers kept debating what exactly they were measuring.
How Scientists Updated the Framework
By the late twentieth century, new biomedical knowledge had outgrown Selye’s original model. One key problem: Selye described the final stage of his syndrome as “exhaustion,” implying the body’s defenses simply ran out. Later research showed something more nuanced. It’s not that the defense mechanisms become depleted. Rather, the stress hormones themselves, the very chemicals meant to protect you, start causing damage when they stay elevated too long.
To capture this idea, researchers introduced the concept of allostasis, meaning the body’s ability to maintain stability through active change. Unlike the older notion of homeostasis, which imagines a fixed set point the body returns to, allostasis describes a dynamic system that constantly adjusts. When the system works well, hormones like adrenaline and cortisol surge briefly, help you adapt, and then recede. When the system is chronically activated, the result is allostatic overload: wear and tear on the cardiovascular system, the brain, the immune system, and metabolism.
In this updated framework, Selye’s alarm stage becomes the process of adaptation. His resistance stage reflects the protective benefits of that adaptation. And his exhaustion stage is reinterpreted as allostatic overload, where the body’s own protective chemicals have been running at harmful levels for too long. The practical difference matters. It shifts the focus from “how much can you endure before you break” to “what happens when your body’s stress chemicals never turn off.”
Stress as a Modern Way of Being
One of the more thought-provoking insights from historians of science is that being “stressed out” is a relatively recent way to understand yourself. The physiological machinery is ancient. Humans 2,000 years ago had the same hormonal surges, the same racing hearts, the same gut reactions. But they didn’t interpret those sensations as “stress.” They might have described fear, grief, exhaustion, or divine punishment. The idea that there is a single unified state called stress, one that connects a tight deadline to a marital conflict to chronic pain, only became part of how people understand themselves in the mid-twentieth century.
This doesn’t mean stress is imaginary. The biology is real and measurable. But the concept is culturally shaped. The social practices in which stress responses are embedded vary across times and cultures. What counts as stressful, how people express it, and what they believe should be done about it are all influenced by the society they live in. Selye’s 74-line letter in 1936 didn’t just name a biological process. It gave the modern world a new lens for interpreting human experience, one that has proven almost impossible to put back in the box.