Your body has an alarm system designed for short, obvious threats. Within seconds it sharpens your senses, speeds up your breathing and prepares your muscles to move.

Stress is that alarm responding to something real in front of you, like a deadline or an argument, and it usually fades once the problem is solved or the day is over.

Anxiety is the same alarm staying switched on after the problem has gone, or starting up with no obvious cause at all, which is what people mean by anxiety for no reason.

It is extremely common. In a national survey of about 31,000 US adults, nearly one in four felt nervous, anxious or on edge on at least some days in the previous two weeks.

The alarm is not only in your head. Shaking hands, a knotted stomach, sweating, short breath and a tight chest are all genuine physical changes that the alarm produces.

Big, unexpected and dangerous events are the strongest triggers. In a study of 7,322 adult twins, events rated high in danger or loss were the ones that predicted new periods of anxiety.

The loop is what keeps it going. Because the body changes feel frightening, the brain reads them as further evidence of danger and turns the alarm up again.

The encouraging part is that this loop can be taught to stand down. Your body learned the anxious pattern through repetition, and it can learn a calmer one with practice.

The system behind anxiety symptoms is the same one that helps you jump back from a car you did not see. It is fast and powerful, and it is designed to switch off again once the moment has passed.

A US health agency sums up the difference simply. Stress is a response to something outside you and fades once it is resolved. Anxiety is your own reaction that can keep going even when there is no threat right now.

“Anxiety attack” is an everyday phrase, not a medical term. Most people use it for a wave of dread with a racing mind, tight chest, shaky hands, fast breathing, sweating or a knotted stomach, often building over minutes or hours.

A panic attack is a sharper, more sudden surge that peaks within minutes, and more than one in five US adults has had at least one. It gets its own page. This one covers the slower, on-edge version that tends to track stress.

The alarm travels two ways. The fast route is a burst of nerve signals and adrenaline that arrives within seconds, which is why your hands shake, your palms sweat and your breath speeds up before you have even named the problem.

The slower route is a chain of hormones that builds over the next 20 to 40 minutes and can take an hour or more to settle, keeping you alert and ready, which is useful for a real threat and exhausting when there is none.

A purely mental task is enough to set it off. In a study of 260 healthy men asked to give a speech and do mental maths in front of a panel, stress and anxiety ratings were highest during the task itself, alongside a rise in stress hormone.

A review of 208 laboratory studies found that the tasks that hit hardest were the ones where people had little control and felt judged by others, and that mix is also a fair description of many ordinary working days.

You do not need a dramatic event to feel anxious. In a national survey, 56% of adults with higher stress said they had felt nervous or anxious from stress in the past month, against 12% of those with lower stress.

Smaller strains also accumulate. In a long-running study of 2,902 adults, men with four or more recent life events were far more likely to develop a lasting anxious spell than men with fewer, so more pressure meant more risk.

Uncertainty is the other important ingredient. Laboratory studies that compare a predictable threat with an unpredictable one find that a clear threat produces a short burst of fear, while an unclear one produces a long, low hum of anxiety.

That hum is often what “anxiety for no reason” is. The reason is real but spread out, like an open-ended worry, a job that could change or a week of small unknowns, and the brain keeps the alarm on because it cannot tell when to stop.

Sleep is the biggest everyday amplifier. Pooled lab studies show a full night without sleep reliably raises anxiety the next day, and a large study found even modestly shorter nights went with more anxiety the following day.

Caffeine can mimic the alarm directly. At doses around five cups of coffee, it raised anxiety in healthy adults as well as in people prone to panic. Energy drinks and pre-workout powders can pack a lot into one serving.

Screens feed it too. After a US news tragedy, people who spent six or more hours a day on coverage reported more acute stress than some who were actually there. Hours of scrolling bad news keep the alarm fed.

Hormones and medicines play a part as well. In a study of 2,956 midlife women, those who began calm were more likely to report high anxiety around menopause. Some cold remedies, steroids and stimulant medicines can also bring on jitters, so stress is rarely the only cause.

What you do after the stress matters. In a lab study of 54 adults, those told to worry after a stressful task took longer to feel better than those given a simple distraction.

Avoiding things teaches the same lesson. Each time you skip the call or leave the room, the brain learns the situation was dangerous, and the alarm fires sooner next time. Staying a little longer is how that lesson is unlearned.

Change is well supported. Pooled across 41 trials and 2,843 people, structured talking therapy eased anxiety more than a placebo. In a month-long trial of 108 adults, five minutes a day of breathing with long exhales lifted mood more than mindfulness did.

You do not have to guess whether you need help. A US expert panel now advises that adults under 65 are asked about anxiety at routine check-ups, using a short questionnaire.

One belief deserves retiring: that anxiety attack symptoms are caused by breathing too fast, and a paper bag fixes them. In a careful trial of 115 patients, a fake version of the over-breathing test brought on the familiar symptoms in most people who reacted to the real one.

When the same patients were tracked during real attacks, their breathing shifted in only about a third of attacks, slightly, and only after the attack had started. Fast breathing is part of the alarm, not the cause of it.

The data also disagree with themselves. Across 49 lab studies, how stressed people felt matched their stress hormone rise in only about one in four. Your feelings and your body do not always move together.

And the link is not the same for everyone. In the study of 2,902 adults, the number of life events predicted anxiety in men but not in women. Stress clearly matters, but how much it matters varies a lot from person to person.