Why does stress show up in my body?

Stress is, before it is anything else, a coordinated bodily response. Within seconds, the heart rate climbs, the breath shifts higher, the muscles ready themselves, and the gut quiets. These changes are mediated by two systems running in parallel: a fast sympathetic-adrenal-medullary wave and a slower hypothalamic-pituitary-adrenal cascade. The response is adaptive when the demand is acute. It becomes costly when it does not have time to settle.

Written and reviewed by Natalia Cajide, Registered Psychologist (AHPRA PSY0002474316). 5 min read. Published 7 June 2026. Last reviewed 7 June 2026. Next review 7 June 2027.

Need help right now? Crisis 000 · Lifeline 13 11 14 · Beyond Blue 1300 22 4636 · Suicide Call Back 1300 659 467

Two waves, running in sequence

When I describe to people what is happening in their body during stress, the order most often surprises them. The body responds before the conscious thought arrives. The processing happens in structures that sit beneath the parts of the brain we use to think about thinking, in milliseconds, and the conscious experience of "I feel stressed" tends to follow rather than precede the bodily mobilisation.

The mobilisation runs in two waves. The first is fast. The sympathetic nervous system releases adrenaline and noradrenaline, and within seconds the heart rate climbs, the breath shifts higher into the chest, blood redirects toward the large muscles, the pupils widen, and digestion slows. This is the sympathetic-adrenal-medullary wave, often shortened to SAM. It is the body preparing to do something.

The second wave is slower. The hypothalamus releases a signal that travels to the pituitary gland, which signals the adrenal glands, which release cortisol. This is the hypothalamic-pituitary-adrenal axis, the HPA axis. Its timescale is minutes rather than seconds. Cortisol mobilises glucose, sharpens attention to threat, and quiets functions the system has decided are not needed at this moment, including some immune activity and some digestion.

Both waves are time-limited and designed to peak and then to fall. The system that does the falling is the parasympathetic branch of the autonomic nervous system, sometimes called the brake. The body that is wound up needs the brake to engage. The body that cannot engage the brake stays wound up.

Why people feel it where they feel it

The reason stress shows up in the chest for some people and in the gut for others has to do with which parts of the autonomic system are most reactive in that particular body. The cardiovascular system carries some of the load through heart rate and breath, and heart rate variability has been described as the most reliable available index of the parasympathetic brake (Peabody et al., 2023). The digestive system carries some of the load through gut motility and microbiome changes, an area where the evidence is still emerging but where 2025 reviews suggest meaningful gut-brain effects from even acute stress (Rosell-Cardona et al., 2025). The muscular system carries some of the load through held tension, which is why headache and shoulder pain are common stress signatures. The immune system carries some of the load through inflammatory shifts.

None of this is hypochondria. None of this is "all in your head," and the distinction between mind and body in this domain is, frankly, less useful than the culture often suggests. The body and the brain are running the response together, and the experience of stress as a bodily thing is an accurate report of what is actually happening.

When the brake stops engaging

The trouble arises when the response, designed to be acute and time-limited, becomes chronic. When cortisol stays elevated. When the brake engages partially or not at all. When the body does not have time to return to baseline before the next demand arrives. The model that captures this is allostatic load, the cumulative cost to the body of repeatedly mounting a stress response without enough recovery in between (Juster, McEwen, & Lupien, 2010).

Allostatic load is what is happening, in the body, when a person describes feeling "wired but tired," or when sleep does not restore, or when minor illnesses keep arriving, or when digestion is consistently disturbed. The body is not malfunctioning. It is doing what it was designed to do, in a situation that does not have the off-ramp the design assumed.

What the body actually responds to

The good news, if there is one, is that the brake can be engaged with input the body recognises. Slow breathing with an exhale longer than the inhale increases vagal activity within a few breaths, and a 2022 systematic review and meta-analysis confirmed this effect across studied populations (Laborde et al., 2022). Brief structured breathing practices, including a five-minute daily cyclic-sighing protocol, have been shown in a 2023 randomised trial to reduce respiratory rate and improve mood across a month, more than a comparable period of mindfulness meditation in healthy adults (Balban et al., 2023). The mechanism is not exotic. The breath has a direct line to the parasympathetic system, and the parasympathetic system is the one the body uses to settle.

The body's role in stress is not a side effect of the real action happening in the mind. It is much of the action, much of the time, and treating the body as the place where the work begins, rather than as the downstream consequence of how you are thinking, often produces shifts that thinking alone has not been able to produce. The body is the first reader of what is happening and one of the most direct routes back to a settled state. The work, when it works, is usually the work of giving the body what it can actually respond to.

This content is general information only. It is not a substitute for individual psychological or medical advice. Reading this does not establish a therapeutic relationship with Equal Psychology or any of their clinicians.