The General Adaptation Syndrome (GAS)

is a foundational theory in stress research, developed by Hans Selye in the 1930s. It describes a universal, three-stage physiological response that the body undergoes when exposed to any significant stressor, whether it's physical (like injury or extreme cold) or psychological (like a demanding deadline or emotional conflict). Selye argued that regardless of the stressor's nature, the body's general response pattern remains consistent.

The three stages of GAS are:

1. Alarm Reaction Stage: This is the body's initial, immediate "fight-or-flight" response to a perceived threat. Upon encountering a stressor, the sympathetic nervous system is rapidly activated. This triggers a cascade of physiological changes: the adrenal glands release stress hormones like adrenaline (epinephrine) and cortisol, leading to an increased heart rate, elevated blood pressure, rapid breathing, muscle tension, and heightened senses. Blood is diverted to muscles, and non-essential bodily functions like digestion and immune activity are temporarily suppressed to mobilize energy for immediate action. This stage is designed for short-term survival and provides a burst of energy to either confront or escape the threat.
2. Resistance Stage: If the stressor persists, the body enters the resistance stage. During this phase, the initial shock of the alarm reaction begins to subside, and the body attempts to adapt and cope with the ongoing stress. Physiological arousal remains elevated, but it's typically lower than in the alarm stage. The body continues to secrete stress hormones, but it tries to normalize its functions while maintaining a heightened state of readiness. Resources are still being mobilized, allowing the individual to endure the stressor for a longer period. While the body appears to be "adapting" externally, this sustained effort consumes considerable energy and resources, and if prolonged, it can start to deplete the body's reserves. Symptoms might become less acute but can include irritability, frustration, and difficulty concentrating.
3. Exhaustion Stage: This is the most dangerous stage and occurs if the stressor continues for an extended period without resolution or adequate recovery. The body's ability to resist stress becomes depleted. The physiological resources that were continuously mobilized in the resistance stage are now exhausted. The symptoms of the alarm stage may reappear, but the body lacks the energy to fight them off. This prolonged over-activation of stress systems leads to "wear and tear" on the body, making it highly vulnerable to illness and disease. Symptoms include extreme fatigue, burnout, depression, anxiety, and a significantly weakened immune system, increasing the risk of stress-related conditions such as heart disease, hypertension, ulcers, and impaired mental health. At this point, the body's adaptive capacity is severely compromised, and if the stress is not alleviated, serious health consequences, or even death, can occur.

Selye's GAS model was groundbreaking for highlighting the physiological mechanisms of stress and demonstrating that chronic stress has tangible, detrimental effects on physical health, moving beyond simply seeing stress as a psychological phenomenon.