Stress is your body and mind reacting to pressure or a threat. The WHO defines it as "a state of worry or mental tension caused by a difficult situation" and calls it a natural human response that prompts us to address challenges and threats. In the body, the brain sets off an alarm: stress hormones such as adrenaline and cortisol are released, the heart beats faster and breathing speeds up. That's useful for a short burst. When the alarm stays on for weeks, it wears you down.
Below: three definitions from health authorities, what happens in the body step by step, why short and long stress are different, the signs and causes, and when stress is a reason to talk to a doctor. This page explains; it doesn't diagnose.
What is stress? Three definitions
| Source | Definition |
|---|---|
| World Health Organization (WHO) | "A state of worry or mental tension caused by a difficult situation." |
| NHS Every Mind Matters | "The body's reaction to feeling threatened or under pressure." |
| National Institute of Mental Health (NIMH) | "The physical or mental response to an external cause, such as having a lot of homework or having an illness." |
All three have the same core: something demands more than feels manageable, and your body and mind respond. NHS Every Mind Matters adds a useful detail: stressful feelings typically happen when we feel we don't have the resources to manage the challenges we face.
What happens in your body when you're stressed
The American Psychological Association (APA) describes the stress response in its overview of stress and the body. In short:
- Your brain rates a situation as challenging or threatening. This can be a real danger or a deadline. The central nervous system plays a key role in reading a situation as potentially threatening.
- The sympathetic nervous system switches on. It's the part of the autonomic nervous system that drives the "fight or flight" response.
- Stress hormones are released. The adrenal glands release adrenaline (epinephrine) and cortisol. A second, slower route runs from the brain through the pituitary gland to the adrenal glands (the HPA axis) and increases cortisol, which makes more energy available.
- Your body gets ready to act. The heart beats faster, you breathe faster, muscles tense and more glucose (sugar energy) enters the bloodstream.
- When the situation passes, the body calms down again. The parasympathetic nervous system, which generally has the opposite effects, helps the body return to its unstressed state.
The German health portal gesund.bund.de adds that processes not needed in the alarm, such as stomach, bowel and bladder activity, are turned down. It also names familiar signs of acute stress before an exam or an important appointment: faster breathing, sweaty hands or feeling that you need the toilet more often than usual.
For the full story of this alarm and what you can do when it fires at the wrong moment, see fight or flight response.
Short-term stress and long-term stress
The difference between a stressful moment and a stressful year matters more than the stress itself.
- Short-term (acute) stress is momentary, like meeting a deadline or slamming on the brakes. APA describes how the body returns to its normal state once the acute episode has passed. Short stress can even help: it focuses you.
- Long-term (chronic) stress means the alarm keeps being triggered over a long period. APA describes this as a long-term drain and "wear-and-tear" on the body: it's less what stress does in one moment and more what continuous activation does over time.
gesund.bund.de describes the body's adaptation to lasting stress in three phases: an alarm phase (hormones, faster heart and breath), a resistance phase in which the body tries to adapt to ongoing pressure and first typical symptoms such as tension can appear, and an exhaustion phase in which performance drops. NHS Every Mind Matters notes that long-term or severe stress can lead to physical, mental and emotional exhaustion, often called "burnout".
Signs of stress
The NHS lists signs in three groups. Not everyone has all of them, and it's not always easy to tell that stress is the reason.
| Physical | Mental | Behavior |
|---|---|---|
| Headaches or dizziness | Difficulty concentrating | Being irritable and snappy |
| Muscle tension or pain | Struggling to make decisions | Sleeping too much or too little |
| Stomach problems | Feeling overwhelmed | Eating too much or too little |
| Chest pain or a faster heartbeat | Constantly worrying | Avoiding places or people |
| Sexual problems | Being forgetful | Drinking or smoking more |
Chest pain can have causes other than stress, so always have it checked by a doctor.
What causes stress?
The NHS says stress is usually a reaction to mental or emotional pressure and is often related to feeling like you're losing control over something, though sometimes there's no obvious cause. Common sources it names:
- Work: pressure at work, unemployment or retirement
- Family: relationship difficulties, divorce or caring for someone
- Money: unexpected bills or borrowing
- Health: illness, injury or losing someone
- Big life events: even happy ones, like buying a house, having a baby or planning a wedding
Whether a situation stresses you also depends on how you see it. gesund.bund.de gives an example: shopping, cooking and cleaning after work feels easy to one person and overwhelming to another. Stress isn't only a long to-do list either; the portal names conflict, too little appreciation and being under-challenged as triggers too.
Is stress bad for you?
Not in itself. The WHO says a little stress is good and can help us perform daily activities, while too much can cause physical and mental health problems. NIMH notes stress can be positive or negative: it may help you meet a deadline, or it may cost you sleep. The problem is stress that's too much, lasts too long or feels out of your control.
Stress or anxiety?
NIMH separates the two like this:
- Stress is generally a response to an external cause, such as a big test or an argument, and goes away once the situation is resolved.
- Anxiety is your reaction to stress. It usually involves a persistent feeling of dread that doesn't go away, and it can be there even when there is no immediate threat.
Both can cause worry, tension, headaches and poor sleep. NIMH suggests getting help if stress symptoms interfere with your everyday life, make you avoid things or seem to be always present.
What is stress management?
Stress management is everything you do to cope with stress and reduce its causes. APA names three building blocks: a healthy social support network, regular physical exercise and enough sleep. The WHO offers a self-help guide, "Doing What Matters in Times of Stress", and says a few minutes a day are enough to practice its skills.
For concrete techniques by time scale (one minute, every day, long term), see our stress relief techniques. If stress has tipped into feeling that everything is too much, start with feeling overwhelmed.
Other meanings of "stress"
This page is about psychological stress. Terms like stress incontinence, stress test and stress fracture are medical topics that have nothing to do with feeling stressed; ask a doctor about them. "Stress and strain" is a pair of terms from physics and engineering.
Understand your stress with the app
AI Meditation: Sleep & Calm has a knowledge session called Understanding Stress and Overload. It explains, in plain words, why stress often builds up at work, why overload feels different from "a lot to do", how perfectionism and poor sleep feed into it, and ends with three thoughts to take with you, including this one: "Stress is a state, not a verdict." For moments when stress is already high, Acute Stress SOS guides you through a longer exhale and a short grounding.
The voices are AI voices, and you can set how long a session lasts within its range. See how the app works, try it for free, no account needed.
When to talk to a doctor about stress
The NHS suggests seeing a GP if you're struggling to cope with stress, if the things you're trying yourself are not helping, or if you'd prefer a referral. NIMH suggests talking to a professional if the symptoms of stress won't go away. If you're in immediate distress, call or text 988 in the US or call Samaritans on 116 123 in the UK.
Your health
This app is a wellness app and does not replace medical advice. If stress lasts for weeks, affects your day or your sleep, or comes with physical symptoms, talk to a doctor. The NHS page on stress lists symptoms, self-help and where to get help.
Sources
All pages accessed on September 25, 2026.
- World Health Organization: Stress, questions and answers (March 30, 2026). Definition, a little stress is good, self-help guide.
- NHS Every Mind Matters: Dealing with stress. Definition, resources, burnout.
- NHS: Stress (page last reviewed March 6, 2026). Symptoms, causes, when to see a GP.
- National Institute of Mental Health: I'm So Stressed Out! Fact Sheet. Definition, stress versus anxiety, when to seek help.
- American Psychological Association: Stress effects on the body (last reviewed October 21, 2024). Nervous system, hormones, HPA axis, acute and chronic stress, stress management.
- gesund.bund.de (German Federal Ministry of Health): Stress (as of January 14, 2026, German). Three phases, processes turned down, appraisal and triggers.
