Stress is caused by demands, external and internal, but only becomes stress once the mind appraises a demand as threatening and one's resources as insufficient to cope. External stressors include major life events, daily hassles, work, money, relationships and environment; internal sources include perfectionism, catastrophising and intolerance of uncertainty. Appraisal is why the same event affects people so differently.
Key terms
- Stressor
- Any demand, external or internal, with the potential to trigger a stress response. The stressor is the trigger, not the stress itself.
- Daily hassles
- The small, repeated frictions of ordinary life whose cumulative load can predict strain as strongly as rare major events.
- Appraisal
- Your judgement of whether a demand is threatening and whether you can cope, which decides how stressful it becomes.
- Intolerance of uncertainty
- A thinking style in which not knowing an outcome feels threatening, amplifying stress from ambiguous situations.
Quick answers
What are the main causes of stress?
External stressors, major life events, daily hassles, work, money, relationships, and environment, plus internal sources such as perfectionism and intolerance of uncertainty. None of them causes stress on its own; your appraisal of the demand is what turns a situation into stress.
Why does the same event stress one person and not another?
Because stress depends on appraisal, not the event alone. We first judge whether a situation is a threat, then whether we can cope. Experience, beliefs, skills, support, and current reserves all shape that judgement, so the same stressor lands very differently for different people.
Are small daily annoyances as harmful as big life events?
They can be. Major events are intense but rare; daily hassles recur constantly, keeping the stress response switched on rather than letting it spike and reset. Their accumulated load can predict strain as strongly as major life events.
The two-part answer: demand plus appraisal
Everyday language treats stress as something that happens to you: a heavy week is stressful, a difficult boss is stressful. That is only half true. As the overview sets out, psychologists distinguish the stressor, the external demand, from stress, the internal response. A cause of stress is therefore never just an event; it is an event that has been judged, by a particular person, in a particular moment, as more than they can comfortably handle.
This is why any honest account of what causes stress has to run on two tracks at once. The first track is the catalogue of stressors: the life events, hassles, pressures and conditions that press on us. The second track is appraisal: the mental process that turns some of those pressures into stress and lets others pass. Skip the second track and stress looks arbitrary. Include it and stress becomes intelligible, even predictable. The rest of this page works through both, then shows how acute and chronic stressors differ in their pattern and their toll.
External stressors: the demands acting on us
External stressors are the demands that originate outside the mind. They range from single, seismic events to the low, grinding friction of ordinary days. Six broad families cover most of them.
Major life events
Large, identifiable changes that force significant readjustment: bereavement, divorce or separation, serious illness, job loss, or moving home. In 1967, Thomas Holmes and Richard Rahe built the Social Readjustment Rating Scale around exactly this idea, ranking life events by the amount of adjustment they demand, with the death of a spouse near the top. Their central insight was that change itself, even change we choose or welcome such as marriage or a new job, is a demand on the system. Notably, positive events appear on the scale too, because they still require adaptation.
Daily hassles
The small, repeated irritations of ordinary life: the commute, the overflowing inbox, misplaced keys, queues, minor conflicts, and the endless small logistics of running a life. Individually trivial, they accumulate. Research following Lazarus and colleagues found that the running total of daily hassles can predict psychological strain at least as well as major life events, precisely because they recur so relentlessly that the stress response rarely gets to reset.
Work and role demands
One of the most common sources of sustained stress: high workload with tight deadlines, low control over how work is done, role ambiguity, long hours, job insecurity, and conflict with colleagues or managers. Work stress is potent because so much of it is chronic rather than acute, present day after day, and because it often combines heavy demand with limited power to change the situation.
Financial pressure
Money worries are among the most reported sources of stress, and among the most corrosive, because they touch nearly every other domain: housing, health, relationships, and the future. Financial stress is frequently ongoing and hard to escape in the short term, which is exactly the profile of a chronic stressor.
Relationships and social conflict
Human relationships are a profound source of both support and strain. Conflict with a partner, family tension, caregiving demands, loneliness, and social evaluation, the fear of being judged, all reliably trigger the stress response. Because relationships are enduring, relational stress often runs long, and unresolved conflict can keep the system switched on for weeks.
Environmental stressors
Physical conditions that tax the body and mind: chronic noise, overcrowding, poor sleep environments, extreme temperatures, and unsafe or unstable surroundings. These often work below conscious notice, which makes them easy to underestimate even as they steadily raise the baseline load.
Change is a demand, even good change: one of the most counterintuitive findings from the Holmes and Rahe work is that welcome events, a promotion, a wedding, a new baby, still register as stressors. The system does not respond to whether change is desirable; it responds to whether change requires adaptation. This is why a run of positive milestones can leave people unexpectedly frayed, and why "nothing is wrong" is not the same as "nothing is demanding."
Major life events versus daily hassles
These two families of external stressor behave so differently that it is worth putting them side by side. Major events are dramatic and easy to blame; daily hassles are quiet and easy to dismiss. Yet the quiet ones often do more of the long-term damage.
| Feature | Major life events | Daily hassles |
|---|---|---|
| Examples | Bereavement, divorce, job loss, moving | Commute, inbox, queues, minor conflicts |
| Frequency | Rare and discrete | Constant and repeating |
| Intensity | High per event | Low per event |
| Pattern | Spikes, then eases as you adjust | Persistent background load |
| Visibility | Obvious, easy to attribute | Easy to overlook or dismiss |
| Long-term toll | Significant but often time-limited | Can rival major events through accumulation |
The practical lesson is not to rank one above the other but to notice both. People readily attribute stress to the big, nameable events and overlook the steady drip of hassles that keeps their baseline arousal high. When someone insists nothing major is wrong yet feels permanently frayed, accumulated daily hassles are often the missing explanation.
Internal sources: how the mind manufactures demand
Not every stressor comes from outside. The mind can generate demand of its own, through habitual thinking styles that magnify threat or shrink the sense of being able to cope. These internal sources are important because they travel with us: change the situation and they remain, quietly loading the next one.
Thinking styles that inflate threat
Cognitive habits such as catastrophising (assuming the worst outcome), black-and-white thinking, and rumination (replaying problems without resolving them) all bias appraisal toward threat. They make ordinary demands read as emergencies and keep the stress response engaged long after the trigger has passed, because the mind keeps re-presenting the threat.
Perfectionism
Setting standards that can never quite be met guarantees a chronic sense of falling short. Perfectionism converts ordinary tasks into high-stakes tests and treats normal error as failure, which keeps demand elevated regardless of how well things are actually going. It is a reliable engine of self-generated stress.
Intolerance of uncertainty
For some people, not knowing an outcome is itself deeply threatening. Ambiguous situations, an unanswered message, an undiagnosed symptom, an undecided plan, become sources of sustained stress because the mind treats the open question as a live danger. Since much of life is uncertain, this thinking style creates a broad and steady stream of stressors from situations others would find neutral.
Low perceived control and self-efficacy
Appraisal has two steps, and the second is a judgement about resources: can I cope with this? People who doubt their ability to influence outcomes, or who feel low self-efficacy, appraise more demands as exceeding their resources, so more situations tip into stress. The belief that one cannot cope is, in effect, a stressor multiplier.
The role of appraisal: the deciding factor
If external and internal sources are the raw material, appraisal is the switch that turns some demands into stress and lets others pass. This is the core of the transactional model of stress set out by Richard Lazarus and Susan Folkman in 1984, and it is the single most useful idea for understanding why stress is so personal.
Their model describes appraisal in two steps. In primary appraisal, the mind asks: is this relevant to me, and is it a threat, a challenge, or harmless? In secondary appraisal, it asks: do I have the resources, skills, support, time, energy, to handle it? Stress arises when a demand is judged threatening and resources are judged insufficient. Change either judgement and the same event stops being stressful. A challenging appraisal ("this is hard but I can grow through it") produces a very different state from a threat appraisal ("this could ruin me and I cannot cope").
One deadline, two appraisals
Two colleagues receive the identical brief on a Friday: a major report due Monday. The first has written similar reports before, trusts her manager to be reasonable, and sees a demanding but doable weekend, a challenge appraisal, with resources judged sufficient. Her arousal rises to a useful level and sharpens her focus. The second is new to the role, fears that a poor report will confirm he was a bad hire, and cannot see how the weekend adds up, a threat appraisal, with resources judged short. His stress response switches on hard and stays on, eroding the very concentration he needs.
The brief is identical. The stress is not. The difference lives entirely in appraisal, shaped by experience, belief, and perceived resources, which is exactly why the most effective ways to reduce stress often work by changing how a demand is seen or resourced rather than by removing the demand itself.
Appraisal also explains a subtler point: because it is a judgement, it is modifiable. Skills, evidence of past success, social support, and reframing all shift appraisal toward challenge and away from threat. That is the psychological foundation beneath most evidence-based approaches to managing stress.
Acute versus chronic stressor patterns
Stressors also differ in their timing, and this matters as much as their content. An acute stressor is a discrete demand with a beginning and an end: a near-miss in traffic, a difficult phone call, a single exam. The stress response spikes and, once the demand passes, switches off, and the body returns to baseline. This is the pattern the fight-or-flight system was built for.
A chronic stressor is ongoing and unresolved: a strained marriage, insecure work, sustained money trouble, long-term caregiving, or a noisy home that never quietens. Here the demand does not pass, so the stress response never fully shuts off. Cortisol and arousal stay elevated, recovery stays incomplete, and the wear accumulates, a load the physiologist Bruce McEwen described as allostatic load, the cumulative cost of the body staying switched on to keep adapting. As the overview explains, chronic stress is responsible for most stress-related harm, and its defining feature traces directly back to the stressor: it is a demand that will not end.
This is why the same category of stressor can be benign or damaging depending on its pattern. A single argument is an acute stressor and usually harmless; a relationship of unresolved conflict is a chronic stressor and genuinely corrosive. When assessing what is causing stress, the timing of a stressor, does it resolve or does it persist, is often more predictive of harm than its headline severity. The types of stress page works through these patterns in detail.
Common misconceptions about what causes stress
Stress is caused by the situation, full stop.
The situation is only the stressor. Stress arises from appraisal: how threatening the demand seems and whether you feel able to cope. That is why the same situation stresses one person and energises another, and why changing the appraisal can reduce stress without changing the situation.
Only big, negative events cause real stress.
Positive events such as a wedding or promotion still demand adaptation and register as stressors, and the steady accumulation of small daily hassles can predict strain as strongly as major events. Severity is not the only thing that matters; persistence often matters more.
If you are stressed, something must be seriously wrong.
Often the cause is an accumulation of ordinary demands and thinking styles rather than a single crisis. People can feel permanently frayed while insisting nothing major is wrong, because daily hassles and internal sources such as perfectionism are doing the loading quietly.
Continue reading
Sources
- Lazarus RS, Folkman S. Stress, Appraisal, and Coping. Springer; 1984.
- Holmes TH, Rahe RH. The Social Readjustment Rating Scale. Journal of Psychosomatic Research. 1967;11(2):213-218.
- McEwen BS. Physiology and neurobiology of stress and adaptation: central role of the brain. Physiological Reviews. 2007;87(3):873-904.
This page is educational and is not medical advice. It does not diagnose any condition. If stress is affecting your health, work, or relationships, speak with a qualified healthcare professional.