The General Adaptation Syndrome

Selye noticed that the body reacts to almost any sustained stressor the same way, regardless of what the stressor actually is. In the alarm stage, the body detects a threat and the nervous system triggers the fight, flight, or freeze response: adrenaline surges, heart rate and breathing speed up, blood sugar rises, and blood flow shifts toward muscles and away from digestion. This happens in seconds because it runs through fast neural and hormonal pathways built for immediate survival, not careful planning. If the stressor continues, the body moves into resistance, where it keeps pumping out stress hormones like cortisol to stay functional at a heightened level. This works, but it draws down a limited pool of physiological resources rather than creating new ones.

That is why people often get sick right after a crisis passes rather than during it: during resistance, the body is spending everything it has just to keep going, holding illness at bay by sheer effort. Once the stressor ends or resources run out, that effort can't be sustained, and the body's defenses drop just as it finally has room to react. If the stressor persists long enough, the person enters exhaustion: the resource pool is depleted, the immune system weakens, and real physical damage appears, from infections to cardiovascular strain.

This stage model sets up the rest of the unit: it explains why chronic stress, not just intense stress, is what wears down health, and it motivates looking at what buffers people against reaching exhaustion, such as coping resources and social support, and what treatments can help restore the body once it gets there.