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Psychology · Foundations

Stress

9 min read 5 practice questions
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On this page 9 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Worked example
  6. Key takeaway
  7. Quick check
  8. Study tools
  9. Sources & references

In 30 seconds

is the body's response to demands or threats. The triggers — stressors — range from to major life events to . In a real emergency the alarm is useful: Walter Cannon named it the , and Hans Selye mapped its longer course as the general adaptation syndrome. The alarm gets expensive when it keeps ringing: chronic stress wears on the body. Not all stress is bad, though. Selye called the beneficial kind . Stress is the body's alarm system — useful, and costly when overused.

Why this matters

Stress is not a classroom abstraction; it is the body's oldest alarm system, and everyone lives with it. Academically, the topic connects psychology to biology: fight-or-flight and the general adaptation syndrome are the bridge between what you feel and what your body does. Practically, understanding stress changes how you read your own experience — a racing heart before a presentation runs on the same machinery that once fueled a sprint from a predator, and knowing that makes the feeling less mysterious. It also gives you a steadier frame for health claims: chronic stress is real, and so is the honest point that not all stress is harmful. How people manage stress belongs to the next topic; this lesson is the foundation it builds on.

The college version

What stress is

The working definition is response-based: stress is the body's reaction to demands or threats. Hans Selye, the endocrinologist who pioneered stress research, defined stress as the response of the body to any demand, whether caused by pleasant or unpleasant conditions (Selye, 1976). The APA Dictionary of Psychology agrees: stress is the physiological or psychological response to internal or external stressors, touching nearly every body system. The word response is the heart of it — stress is what the body does about the event, not the event itself. Original example: Maya's phone buzzes with the acceptance email she has awaited for months; her heart pounds — the identical rush she felt last month when a stranger's car slid through the intersection in front of her. Good news and near-miss: one body, same alarm.

Stressors: what sets off the alarm

A is any event, force, or condition that results in physical or emotional stress. Stressors come in three families. Daily hassles are the minor irritations of ordinary life, and they build on one another, leaving people just as stressed as major events (Kanner, Coyne, Schaefer, & Lazarus, 1981). Original example: Priya's bus is late, her coffee lid pops off in her bag, and the office printer jams twice — nothing catastrophic, everything cumulative. Major life events are changes that demand significant readjustment, from moving house to a new job to a divorce (Holmes & Rahe, 1967). Original example: Marta and her partner move to a new city the same month both start new jobs — a chosen move, and still a stretch of stress. Chronic strain is the third family: conditions that persist over an extended period — long-term unemployment, unrelenting caregiving. Original example: Deniz has commuted three hours a day for two years to a warehouse job he cannot afford to leave.

The stress response: fight-or-flight

Walter Cannon, a Harvard physiologist, first articulated and named the body's immediate reaction to a perceived threat: the fight-or-flight response (Cannon, 1932). Faced with danger, the sympathetic nervous system and adrenal glands flood the body with epinephrine and norepinephrine: the heart speeds up, breathing quickens, pupils dilate, blood flows to the muscles, and digestion slows. The point is energy mobilization — the body prepares to fight or flee. Original example: Nia is crossing the street when a car runs the red light and swerves toward her; within a second her heart pounds and her breath shortens as she jumps back onto the curb. The honest note: this machinery is ancient, tuned for physical emergencies like predators, falls, and fights. Most modern stressors — a deadline, an argument, an inbox — do not call for fighting or fleeing, so the alarm rings with no physical action to follow.

The general adaptation syndrome: Selye's three stages

Selye asked what happens when stress does not end quickly. His answer, the , describes three stages of responding to prolonged stress (Selye, 1936; 1976). The alarm reaction is the body's immediate mobilization on facing a threat — roughly the fight-or-flight response. Original example: a lifeguard hears a scream from the pool and is instantly alert, heart racing. The stage of resistance follows if the stressor continues: the initial shock wears off, the body adapts and keeps functioning, yet remains on alert, ready to respond with less intensity. Original example: by the second week of final exams, the first-day panic has faded, but the student sleeps lightly and stays keyed up. Exhaustion arrives if the stressor drags on long enough: adaptation fails, resources are depleted, and the body's resistance breaks down — illness and disease become more likely. Original example: after five months of caring for a sick parent, Rosa feels wrung out, sleeps poorly, and catches every cold that passes through her household.

Stress and health: when the alarm keeps ringing

The stress response is built for short emergencies, not for years of low-grade ringing. When the reactions that compose it are chronic, or frequently exceed normal ranges, they produce cumulative wear and tear on the body (McEwen, 1998). The mechanisms are concrete: sustained elevated levels of the stress hormone cortisol can weaken immune system functioning, leaving a person more open to infection and disease, and blood pressure that stays high under prolonged strain can take a toll on the heart. Original example: a bakery owner running a six-day-a-week shop for years is winded on the stairs and catches every flu his staff brings in — the bill for an alarm that has not fully stopped ringing since he opened. What people do about chronic stress — coping — is its own topic; this lesson only describes what the alarm does.

The honest note: eustress, and the honest framing

Not all stress is bad. Selye pointed out that stress can be a positive, motivating force, and he gave the good kind a name: eustress, from the Greek eu, meaning good (Selye, 1974). The APA Dictionary defines eustress as the positive stress response that comes from challenging but attainable and worthwhile tasks, generating fulfillment and high performance. Original example: a violinist feels a flutter of nerves before her first solo recital and uses the extra energy to play with more focus and finish stronger than in rehearsal. The harmful kind, , overwhelms. That leads to the honest framing of this lesson: stress is the body's alarm system. It is useful because it mobilizes you in genuine emergencies, and expensive because every alarm costs something — the bill comes due when it rings too often or too long. Stress is not the enemy. It is a tool with running costs.

Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Stress is the body's alarm system, and the alarm does one job: it tells you something demands your attention. When it sounds, your heart speeds up, your breath quickens, and your muscles tense — that rush is fuel, and it is genuinely useful when the danger is real. The catch is that the alarm was designed for a world of immediate physical dangers: predators, falls, fights. Modern life sets it off with deadlines, arguments, and inboxes — situations where neither fighting nor fleeing helps, so the fuel gets spent on nothing. Ring the alarm constantly and it wears on the body, the way a doorbell that never stops eventually wears on the house. And the alarm is not always bad news: eustress is the good kind, the buzz from challenges you chose, which sharpens you instead of draining you.

Picture it like this

Think of a smoke detector. A working one sits quietly for years, then screams the instant smoke appears — that is its job, and a screaming detector in a real fire is a lifesaver. Stress is the body's smoke detector: it senses a demand or threat and raises the alarm with a burst of energy and alertness. A home needs its detector; a body needs its alarm.

Where the picture stops working

A smoke detector can be silenced with a button or have its battery removed; the body's stress alarm cannot be switched off at will — once a threat is perceived, the response runs on its own. A detector signals one clear danger, while stress responds to anything appraised as demanding, pleasant or unpleasant. And a detector that goes off constantly is merely annoying, while a constantly ringing stress alarm does measurable wear on the body. The detector is also a device you can calibrate; the body's alarm is largely automatic, which is why understanding it matters.

Worked example

Leo, a night-shift nurse, hears a crash from the waiting room at 2 a.m. Instantly his heart pounds and his breath shortens — the fight-or-flight response Walter Cannon described, mobilizing energy before Leo has even decided what to do. The crash was a vending machine tipping over; no one is hurt, and the arousal fades within minutes: an alarm that rang, did its job, and stopped. Leo's other stressor does not stop. For a year, his mother's care has fallen on him, and the demands are unrelenting. Early on, the constant worry kept him wired — an alarm reaction that never quite switched off. Over the months his body adapted, sleeping lightly and staying on edge — Selye's stage of resistance. Lately he wakes exhausted, catches every cold that moves through the ward, and snaps at colleagues; his resources are running down, the stage of exhaustion. The same alarm that saved the vending-machine moment is wearing him out by never fully silencing. The lesson is not that stress is bad. It is that the alarm is useful in emergencies and expensive when it never stops.

Key takeaway

Stress is the body's alarm system: a useful, whole-body response to demands and threats that becomes expensive when it rings too often or too long — and, as Selye's eustress shows, not every alarm is bad news.

Quick check

3 questions here, of 5 in this lesson’s practice set. Answers stay hidden until you check.

Question 1 of 3foundational

A psychology text says stress is the body's response to any demand, whether pleasant or unpleasant. Which researcher is the source of this working definition?

Choose an answer, then check it.
Question 2 of 3foundational

Which researcher first articulated and named the fight-or-flight response?

Choose an answer, then check it.
Question 3 of 3intermediate

Priya's morning is a string of small frustrations: the bus is late, her coffee lid pops off in her bag, and the office printer jams twice before her first meeting. Which term best describes these stressors?

Choose an answer, then check it.
Practice all 5

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Practice this lesson
Study tools & related lessonsYou’ll learn to · Common mistakes · Easily confused · Key vocabulary · Related

You’ll learn to

  • Define stress as the body's response to demands or threats, and attribute the working definition to Hans Selye.
  • Distinguish daily hassles, major life events, and chronic strain as types of stressors, with an original example of each.
  • Explain the fight-or-flight response, name Walter Cannon as the researcher who identified it, and analyze why the response often mismatches modern life.
  • Describe the three stages of Selye's general adaptation syndrome — alarm, resistance, and exhaustion.
  • Explain, factually, how chronic stress wears on the body, and distinguish eustress from distress with an original example.

Common mistakes

  • Stress is just a feeling of being overwhelmed or anxious.

    The feeling is only the part you notice. Stress is a whole-body response — physiological and psychological — involving changes in nearly every system of the body, as the APA Dictionary describes.

  • Only bad events cause stress.

    Selye's definition covers any demand, pleasant or unpleasant. A wedding, a promotion, or a long-awaited move can trigger the same response as a setback — which is exactly why the body, not the event's label, defines stress.

  • Fight-or-flight means you literally fight or run away every time.

    It is the body's arousal pattern — heart, breath, muscles — preparing for physical action. Most modern stressors call for neither fighting nor fleeing, so the response fires with no physical action to match.

  • All stress is harmful and should be avoided.

    Eustress, from challenging but attainable tasks, is beneficial and energizing. The wear-and-tear story belongs to chronic stress — the alarm ringing too often or too long — not to stress itself.

Easily confused

Eustress vs. Distress

Both are stress, but eustress comes from challenging yet attainable demands and fuels fulfillment and performance, while distress overwhelms the body's capacity to adapt and drains performance and health.

Acute stressors vs. Chronic stressors

Acute stressors are brief focal events, like a near-miss on the street; chronic stressors persist over a long period, like a years-long grinding commute, and it is the chronic kind that produces cumulative wear and tear.

Fight-or-flight response vs. The alarm reaction of the GAS

Both describe the body's immediate mobilization in the face of a threat, but fight-or-flight names the sympathetic arousal itself, while the alarm reaction is the opening stage of Selye's longer three-stage sequence of responding to prolonged stress.

Key vocabulary

stress
The body's physiological and psychological response to demands or threats — the working definition, attributed to Hans Selye, covers any demand, pleasant or unpleasant.
stressor
Any event, force, or condition that results in physical or emotional stress; stressors include daily hassles, major life events, and chronic strain.
daily hassles
The minor irritations and annoyances of everyday life that build on one another and can leave people just as stressed as major events.
chronic strain
A stressor that persists over an extended period, such as long-term unemployment or unrelenting caregiving demands.
fight-or-flight response
The rapid, whole-body arousal pattern first articulated and named by Walter Cannon, in which the sympathetic nervous system mobilizes the body to fight a threat or flee from it.
general adaptation syndrome (GAS)
Hans Selye's three-stage account of the body's response to prolonged stress: alarm reaction, stage of resistance, and stage of exhaustion.
eustress
The beneficial kind of stress, named by Selye, arising from challenging but attainable tasks and associated with fulfillment and high performance.
distress
The harmful kind of stress, in which demands overwhelm the body's ability to adapt and performance, well-being, and health decline.

Sources & references

  1. Psychology 2e, Section 14.1: What Is Stress? — OpenStax, Rice University
  2. Psychology 2e, Section 14.2: Stressors — OpenStax, Rice University
  3. Psychology 2e, Section 14.3: Stress and Illness — OpenStax, Rice University
  4. APA Dictionary of Psychology — stress — American Psychological Association (APA Dictionary of Psychology)
  5. APA Dictionary of Psychology — fight-or-flight response — American Psychological Association (APA Dictionary of Psychology)
  6. APA Dictionary of Psychology — general adaptation syndrome (GAS) — American Psychological Association (APA Dictionary of Psychology)
  7. APA Dictionary of Psychology — eustress — American Psychological Association (APA Dictionary of Psychology)
  8. APA Dictionary of Psychology — stressor — American Psychological Association (APA Dictionary of Psychology)

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Researched 2026-08-22

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