Stress is described so loosely in general use that the underlying physiology gets lost. The mechanism is specific and worth knowing.
Two systems, different speeds
The fast response runs through the sympathetic nervous system, releasing adrenaline within seconds.
Heart rate rises, airways open, blood is redirected to muscles, glucose is released, digestion is suppressed.
The slower response runs through a hormonal cascade ending in cortisol release from the adrenal glands, taking minutes to build and persisting far longer.
Cortisol mobilises energy, modulates immune function and affects mood and memory.
Why it exists
The response is an energy mobilisation system for acute physical demand.
Everything it does makes sense for a short intense episode requiring immediate physical action.
It is fast, effective, and designed to switch off.
The feedback loop
Cortisol acts back on the brain to shut down its own production, which is a negative feedback system keeping the response self-limiting.
Chronic activation appears to alter the sensitivity of this feedback, which is one proposed mechanism for why prolonged stress has different effects from acute stress.
Research on this is active, and the specifics are more contested than popular accounts suggest.
What chronic activation is associated with
Stated as association because most human evidence is observational.
Cardiovascular effects through sustained blood pressure elevation.
Metabolic effects through sustained glucose mobilisation.
Immune modulation, with effects that vary by duration and context rather than being simply suppressive.
Sleep disruption, which then compounds everything else.
And effects on mood and cognition that overlap substantially with anxiety and depression.
The controllability finding
One of the more robust results in the whole field.
The same objective stressor produces different physiological and psychological effects depending on whether the person has control over it.
Predictability has a similar effect — a known stressor is tolerated better than an unpredictable one of equal magnitude.
Which is why workplace research consistently finds that high demand combined with low control is the damaging combination, rather than high demand alone.
It also suggests that where control cannot be increased, increasing predictability sometimes can be.
What actually reduces the response
Physical activity uses the mobilised energy for its intended purpose, and the evidence for exercise affecting stress and mood is among the strongest in the area.
Slow breathing, particularly with extended exhalation, engages the parasympathetic system and reduces heart rate measurably. The effect is real, modest and immediate.
Social contact has substantial observational evidence behind it, and the mechanisms proposed include both physiological and practical support.
Sleep, which is both affected by stress and one of the strongest determinants of tolerance for it.
What is oversold
Cortisol has become a marketing term attached to products claiming to reduce it.
Cortisol is necessary. It follows a daily rhythm, peaking shortly after waking. Reducing it generally is not a coherent goal.
Home testing of cortisol is offered commercially and is difficult to interpret without clinical context, since values vary enormously by time of day and situation.
The line worth drawing
Ordinary stress responds to the things above.
Persistent anxiety, panic attacks, inability to function, or physical symptoms without an obvious cause are reasons to see a doctor rather than to try harder at stress management.
Several medical conditions present as stress symptoms, and distinguishing them requires assessment rather than self-management.
Acute against chronic
The distinction that determines whether the response is useful or harmful.
Short-term stress responses improve performance on some tasks, enhance certain immune functions and consolidate memory of the event.
Which is why the finding that all stress is harmful is wrong, and why the concept of beneficial short-term stress appears in the research literature.
The harm associated with stress is essentially all associated with chronicity — the response remaining activated without resolution.
Which suggests the useful question is not how to reduce stress but how to complete the response, and physical activity is the most direct way of doing that.
Burnout
Defined in occupational terms rather than as a medical diagnosis in most classification systems.
The components generally identified are exhaustion, mental distance or cynicism about the work, and reduced professional efficacy.
Which locates it in the relationship between a person and a job rather than in the person, and that framing has consequences for what interventions are appropriate.
Individual-level interventions show smaller effects in reviews than organisational ones, which is consistent with the definition and inconvenient for employers.
Mindset findings
An area with interesting results and contested replication.
Studies have reported that framing the stress response as helpful — the racing heart as preparation rather than as threat — changes physiological measures and performance.
The effects reported are modest, and some of this literature has faced replication questions.
The reframe costs nothing to try and the confidence with which it is promoted exceeds the evidence.
Where to get help
Occupational health services, employee assistance programmes and general practice are all routes, and each has different limits worth knowing before using them.
None of what is written here substitutes for assessment by a clinician who can actually examine you.