In 1936, a young Hungarian endocrinologist named Hans Selye published an eight-hundred-word paper in the journal Nature that would permanently change how medicine and psychology understood stress. He had noticed something strange in his experiments: regardless of what kind of harmful stimulus he exposed rats to — cold, heat, excessive exercise, toxic substances — their bodies showed a remarkably similar pattern of response.
The specific threat didn’t seem to matter. The body had one response for all of them.
He called it the General Adaptation Syndrome (GAS).
The Three Stages of GAS
Stage 1: Alarm Reaction
The body detects a stressor and mobilizes. The hypothalamus triggers the adrenal glands to release adrenaline and cortisol. Heart rate increases, blood pressure rises, digestion shuts down, and energy is redirected to muscles and the brain. This is the classic fight-or-flight response.
At this stage, the body is actually vulnerable — resistance is temporarily below baseline as all resources are mobilized for the emergency. This is why you sometimes don’t notice pain or exhaustion until after a crisis passes.
Stage 2: Resistance
If the stressor continues, the body shifts into sustained adaptation. Cortisol production stabilizes at a higher level. The body appears to cope — you function, you manage, you handle it. From the outside, everything looks fine. This is what most chronically stressed people live in for months or years.
But Selye’s crucial observation was this: maintaining the resistance stage costs resources. The body is burning through its adaptive reserves. The immune system is suppressed. Repair processes are deprioritized. Inflammation builds. The body is coping — but it’s paying for it.
Stage 3: Exhaustion
If the stressor persists long enough, the body’s adaptive reserves are depleted. The resistance stage collapses. What follows is a systemic breakdown — burnout, illness, immune failure, depression, and in extreme cases, organ damage. The body has spent everything it had.
Eustress vs. Distress: Selye’s Most Misunderstood Insight
Selye was also the first to distinguish between eustress (positive stress — the kind generated by excitement, challenge, and meaningful work) and distress (harmful stress). Both activate the same physiological response. But eustress is associated with meaning and agency, while distress involves helplessness and threat.
This matters enormously. Two people can face the same objectively stressful situation — a demanding job, a health challenge, a relationship crisis — and have completely different physiological outcomes based on how much control, meaning, and social support they perceive. The stressor is only half the equation.
What This Means for You Practically
Selye’s model has a sobering implication: the body does not distinguish between a work deadline, a toxic relationship, a poor diet, a bad sleep schedule, and a global pandemic. Each one draws from the same adaptive reserve. When you’re already in the resistance stage from work stress, adding relationship stress doesn’t just add to your load — it accelerates depletion.
This is why “stress management” isn’t just about relaxation techniques. It’s about honestly auditing all the stressors in your life and understanding that your body has a budget — and that budget has a limit.
Signs you may be approaching Stage 3: persistent fatigue that sleep doesn’t fix, getting sick frequently, emotional numbness, inability to feel pleasure, a sense of complete depletion. These aren’t signs of weakness. They’re biological signals that the account is overdrawn.
If you recognize yourself in Stage 2 or 3, please take that seriously. A physician can assess the physical picture; a therapist can help you understand and restructure the psychological load. Selye’s research was a warning written in biology — and it deserves to be heard.