A model called the General Adaptation Syndrome (GAS) is commonly used to understand stress as a process with three functional stages:
- Alarm
- Resistance or Adaptation
- Exhaustion
The Alarm Stage
When an animal is first exposed to a stressor, or perceives a threat, the initial response is a state of alarm. The alarm stage is also commonly known as hyperarousal, acute stress response, fight-or-flight response, fight-or-flight-or-freeze response.
The Resistance or Adaptation Stage
If the stressor persists animals enter the second stage. During this stage the animal remains in a state of alarm while trying to find a way of coping with the stress. As an animal tries to adapt to the stressor, vital resources are gradually depleted. It only takes a few days in the resistance and adaptation stage for the immune system to fall into a weakened state.
The Exhaustion Stage
Exhaustion is the third and final stage of the GAS model. At this point, the animal’s resources are eventually depleted and normal function can no longer be maintained. If this stage is prolonged, long-term damage may result as the animal fails to compensate and functioning becomes impaired.