The stress response is a short-term system with a built-in termination signal. Chronic stress is best understood not as a larger version of that response but as a failure of the mechanism that ends it.
The response is designed to self-limit
A threat triggers a hormonal cascade running from the brain to the adrenal glands, ending in the release of cortisol into the bloodstream.
Cortisol acts on receptors in the brain that suppress the signal which started the cascade. The output of the system is also its brake.
Under normal conditions this produces a rise, a plateau and a return to baseline over a period measured in tens of minutes.
Continuous demand prevents the reset
The brake needs an interval without new triggers to complete. If a fresh demand arrives before the return to baseline, the system restarts from an elevated point.
Repeated across days, the baseline itself shifts. The person is not experiencing a stronger response so much as never completing the previous one.
This is why chronic stress is more closely associated with unrelenting low-level demands than with single severe events, which usually resolve.
Receptors become less responsive
Prolonged exposure to a hormone typically reduces the sensitivity of its receptors. In this system, that reduction weakens the very feedback that shuts the response down.
The consequence is a response that is harder to trigger appropriately and harder to terminate, which is a poorer configuration than either high or low output alone.
The same receptor changes affect immune regulation, since cortisol is also the main brake on inflammatory signalling.
Anticipation keeps the system engaged
Humans can activate the response through expectation. A demand scheduled for next week can trigger it repeatedly in the meantime.
Because anticipation has no natural endpoint, the trigger is present continuously rather than in discrete episodes, which removes the recovery intervals the system requires.
This is why uncertainty and lack of control are stronger predictors of chronic stress in research than workload measured on its own.
Why recovery periods do the work
Interventions that reduce chronic stress generally operate by restoring complete recovery rather than by removing all demand, which is rarely available.
Sleep, physical activity and periods of genuine disengagement all allow the cascade to complete, which is a different function from distraction during the demand itself.
Persistent stress that is affecting sleep, mood or physical health warrants clinical assessment rather than management through self-directed techniques alone.