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Hans Selye proposed the general adaptation syndrome (GAS) to describe the body's consistent pattern of responding to stress through three predictable stages: alarm, resistance, and exhaustion. GAS explains how the body mobilizes defenses against perceived threats and why prolonged stress can lead to health problems. This model helps psychologists understand the physiological mechanisms underlying stress responses.

During the alarm stage, the body experiences temporary shock as stress hormones like adrenaline and cortisol are released. Although these hormones prepare the body for quick response, they simultaneously suppress the immune system, increasing vulnerability to infections and illness. Physiological resistance drops below normal levels during this initial phase.

In the resistance stage, the body increases hormone production to defend against ongoing stress. The anti-inflammatory hormone cortisol is released to reduce physical injury effects, and the immune system functions more effectively to combat infections. The body stabilizes its defenses and maintains relatively high efficiency despite persistent stress.

During exhaustion, prolonged stress depletes energy reserves, causing physical and mental fatigue. The body's heightened vulnerability leads to serious health consequences including cardiovascular diseases, immune dysfunction, and potentially mortality. Continuous stress activation without recovery causes irreversible damage to vital organs and systems.

During the alarm stage, stress hormones weaken immune function, increasing infection risk. However, during the resistance stage, the body counteracts this by increasing hormone production and releasing cortisol to reduce inflammation, allowing the immune system to combat infections effectively. This adaptation enables the body to maintain defense despite ongoing stress.

The general adaptation syndrome explains how the body's stress response progresses through predictable stages and why chronic stress becomes harmful. Understanding these stages helps identify when stress transitions from manageable to dangerous, revealing why prolonged stress leads to serious health conditions. This framework guides stress prevention and stress management techniques to interrupt the exhaustion stage.

Cortisol is released during both the alarm and resistance stages but serves different functions. In the alarm stage, it contributes to immune suppression, while in the resistance stage, cortisol acts as an anti-inflammatory hormone that reduces physical injury effects and enhances the body's ability to cope with challenges. This dual role reflects the body's adaptive stress response.