General adaptation syndrome: Selye's three stages, and where resistance runs out

General adaptation syndrome is Hans Selye's three-stage account of how the body reacts to prolonged stress. First comes alarm, a shock followed by a countershock that looks much like fight-or-flight. Then comes resistance, where the body adapts but stays on alert. Then comes exhaustion, where the body's resources run out and illness follows. Selye built the model on rat experiments in the 1930s, and it still shapes how textbooks teach stress, even though it leaves out the mind's side of the story.

Where the idea came from

In the 1930s Hans Selye worked as a young assistant in the biochemistry department at McGill University. He studied sex hormones in rats, but he noticed something odd. Rats exposed to very different harms, extreme cold, surgical injury, hard exercise, and shock, all showed the same three physical changes. Their adrenal glands grew larger. Their thymus glands and lymph nodes shrank. Their stomachs developed ulcers.

Selye concluded that the body answers very different threats with one shared pattern. He called this pattern the general adaptation syndrome. The word general matters. It means the response is nonspecific: the same bodily program runs no matter which stressor starts it. He first described the syndrome in 1936 and presented it in his Heberden Oration of June 2, 1950, published in the British Medical Journal. Selye, a Hungarian-born Canadian endocrinologist who lived from 1907 to 1982, went on to define stress itself as the body's response to any demand, pleasant or unpleasant.

Stage 1: alarm reaction

Alarm is the body's immediate answer to a sudden threat. Selye split it into two quick phases. In the shock phase, the body's resistance drops below normal. Temperature, blood pressure, and muscle tone fall. In the countershock phase, the sympathetic nervous system fires back. Adrenal glands release adrenaline and noradrenaline, and the body rallies to meet the crisis.

This countershock looks much like the fight-or-flight response Walter Cannon described in 1932. Heart rate climbs. Breathing quickens. Muscles tense. Stored glucose enters the blood for fuel. Digestion slows while energy moves to the muscles. Cannon saw this arousal as the body's way to protect homeostasis, the stable inner state the body defends.

Alarm is roughly analogous to fight-or-flight, but the two are not the same thing. Cannon described a rapid response to an intense emotion or perceived threat. Selye described the opening phase of a longer program that continues even when the threat stays for weeks. Exams often test exactly this boundary, so keep the wording strict: roughly analogous, not identical.

Stage 2: resistance

If the stressor continues, the body enters the stage of resistance. The first shock wears off. The body adapts to the stressor, yet it stays on alert and ready to respond much as it did during alarm, only with less force. A parent whose child has been missing for three days still feels deep distress, but the sharp peak of the first hours has passed. The body has adjusted to a higher level of arousal.

A different hormone system now carries the load. The fast sympathetic response fades, and the hypothalamic-pituitary-adrenal axis takes over. The hypothalamus releases corticotropin-releasing factor. That signal prompts the pituitary gland to release adrenocorticotropic hormone. That hormone prompts the adrenal cortex, the outer shell of the adrenal glands, to release cortisol.

Cortisol keeps blood sugar high by building glucose from stored proteins, a process called gluconeogenesis. It also quiets systems the body treats as nonessential during a crisis, such as digestion, reproduction, and parts of immune defense. In short bursts this response helps: extra energy, lower pain sensitivity, and a brief lift in immune readiness. Over weeks, the price grows. Sustained high cortisol weakens immune defense, and high levels often appear alongside depression.

Resistance sounds like recovery, but it is not. Recovery means the stressor ended and the body returned to baseline. Resistance means the stressor continues and the body holds an expensive alert posture. That distinction answers many exam questions on its own.

Stage 3: exhaustion

If the stressor continues longer still, the stage of exhaustion begins. The body's ability to adapt runs out. Hormone supplies dwindle and blood sugar control slips. Immune defense drops hard. Tissues and organs take lasting wear. Illness, disease, and lasting damage follow, and in extreme cases death.

Selye described a clear set of signs at this stage: disturbed sleep, irritability, severe loss of concentration, restlessness, trembling that disturbs movement, fatigue, jumpiness, a low startle threshold, vulnerability to anxiety, depressed mood, and crying spells. These are the signs he recorded in prolonged stress, not a checklist for self-diagnosis. If stress starts to damage your health, talk to a doctor or another health professional about it.

Exhaustion also differs from burnout. Exhaustion is the third stage of Selye's bodily program and can follow any long stressor. Burnout is a work-related phenomenon the World Health Organization classifies with the code QD85, and it is not a medical diagnosis. The two overlap in fatigue, but they belong to different systems: one is a general stress model, the other an occupational one.

Eustress and distress: not all stress harms

Selye argued that stress is not always bad. He named the helpful kind eustress, from the Greek eu for good. Eustress comes from tasks that challenge yet stay within reach, such as an athletic event, a speech, or a hard exam for which you prepared well. It brings a sense of fulfillment and can lift performance. He named the harmful kind distress, from the Latin dis for bad. Distress comes from demands that overwhelm you, and it drags performance down once stress passes an optimal level. Severe test anxiety shows the distress side: worry plus physical symptoms narrow attention and lower scores.

The eustress idea matters for one more reason. Selye defined stress as a response to any demand, pleasant or unpleasant. Good news can raise your heart rate too. What makes the response harmful or helpful is not the demand alone but its size, its length, and whether you can meet it.

What the model gets right, and what it misses

Selye's model earned its place for one achievement. It gave concrete proof that long stress damages the body, and it offered a general account of how that damage unfolds. That account still organizes the stress chapter of textbooks such as OpenStax Psychology.

Its weak point is just as clear. The model is response-based: it tracks the body's physical reactions and largely ignores how people judge threats. Richard Lazarus and Susan Folkman argued in 1984 that appraisal decides much of the outcome. A primary appraisal judges whether an event threatens harm or promises growth. A secondary appraisal judges which coping options exist and how well they work. Two people can meet the same demand and feel very different stress. Our article on locus of control covers a related idea: how much control people expect over outcomes shapes how they answer pressure.

A second caution comes from later physiology. Selye claimed the pattern stays the same for every stressor. Later work found that different stressors can produce somewhat different hormonal profiles, so the nonspecificity claim needs softening. Treat GAS as the body's side of stress, strong on stages and hormones, silent on thought and judgment.

Remember it for the exam

Students meet this topic as a list to memorize, so here is the list, in order, with the three traps that cost marks.

1. 1.Alarm, then resistance, then exhaustion. Alarm itself splits into shock and countershock. If a question offers four stages, it likely counts shock and countershock separately.
2. 2.Alarm runs on adrenaline from the adrenal medulla through fast nerves. Resistance runs on cortisol from the adrenal cortex through the slow HPA axis. Match each hormone to its stage and gland layer.
3. 3.Three traps: alarm is roughly analogous to fight-or-flight, not identical to it; resistance means adapted but still alert, not recovered; exhaustion means depleted adaptation, not the same as occupational burnout.

Put these terms into practice the way the exam tests them. Save alarm reaction, shock, countershock, resistance, exhaustion, eustress, and distress into one bookmark list in Psychology World. Then drill that list with the Question game until each term gives the right answer on first sight.