Almost everyone uses the word “stress” as though it were one thing. I’m stressed about the deadline. My partner’s been stressed this week. That job is so stressful. The word slides between contexts so easily that it’s worth stopping, for a moment, to notice how much it’s actually covering. The stress of an exam due tomorrow and the stress of a failing marriage are presumably not the same kind of experience. The stress of a sudden near-accident on the motorway and the stress of a long-running financial worry presumably do different things to the body. And yet the same word applies to all of them.
The researcher who first tried to impose some order on this was a Hungarian-Canadian endocrinologist named Hans Selye, who did his foundational work at McGill University and later at the Université de Montréal from the 1930s onward. Selye was studying what happened to rats when they were subjected to various kinds of physical stressors — heat, cold, injury, sleep deprivation. He found that regardless of the specific stressor, the rats’ bodies produced a characteristic biological response: a cascade of hormones, including what we now call cortisol, released from the adrenal glands; changes in the immune system; and a series of bodily adaptations he called the General Adaptation Syndrome.
Selye introduced the word “stress” into medical and eventually popular vocabulary. He also introduced a distinction that turned out to be extremely useful and that has shaped the field since: the distinction between eustress and distress.
Two kinds of pressure
Eustress, in Selye’s framing, is useful pressure. It’s the energising kind — the intensity before a performance, the sharpened focus of a challenging project, the concentrated effort of a difficult conversation, the thrill of a moderately risky activity. Eustress is, in moderation, life-enhancing. It produces the feeling of being engaged, of rising to meet a situation, of operating at the top of one’s range. Most of what humans find meaningful — creative work, demanding relationships, worthwhile projects — involves some amount of eustress.
Distress, by contrast, is pressure without resolution. It’s the chronic, unresolved, uncontrollable kind — the grinding worry that doesn’t produce action, the low-grade fear that keeps running even when the immediate trigger is gone, the long-running exposure to circumstances you cannot change. Distress is corrosive. Over time, it produces measurable damage to the cardiovascular system, the immune system, the brain, and the general infrastructure of a human body.
Selye’s distinction was useful partly because it cut against an older intuition that all stress was bad. If stress were uniformly harmful, the advice would be simply to eliminate it from life. But a life entirely without stress would also be a life without engagement, effort, or growth. The question wasn’t how to eliminate stress — it was how to distinguish its two forms, encourage the useful one, and limit the damaging one.
The modern picture
Selye’s framing has been substantially enriched over the decades, though its core insight has held up. Two more recent researchers, in particular, have extended the framework in ways worth knowing about.
Robert Sapolsky, a neuroendocrinologist at Stanford, has spent much of his career studying what chronic stress actually does to the body — most famously in wild baboons in East Africa, which he has observed and sampled over decades, and whose social lives offer a natural experiment in who experiences chronic stress and who doesn’t. His book Why Zebras Don’t Get Ulcers brought this research to popular audiences.
Sapolsky’s central observation is that the human stress response was evolved for a specific kind of threat — an immediate physical emergency. Predator approaching. Injury. Acute shortage of food or water. The response is beautifully engineered for this: instant hormonal cascade, blood redirected from digestion and long-term repair to muscles, heightened alertness, pain suppression. After the emergency ends, the response shuts down, and the body returns to baseline within hours.
The modern problem is that humans now activate this same response in contexts it wasn’t built for — chronic workplace pressure, relationship difficulties, financial worry, social media exposure, traffic. These activations don’t end in a few minutes. They can persist for weeks, months, years. The body is running on emergency settings continuously. And the systems that were supposed to be briefly deferred — immune function, digestive function, reproductive function, cardiovascular maintenance — stay deferred, accumulating wear over time. Zebras, to use Sapolsky’s example, don’t get ulcers because their stress responses switch on briefly when they’re chased by a lion and switch off once they’re safe. Humans get ulcers because their stress responses switch on when they open an email and don’t fully switch off for decades.
The concept of allostatic load, developed by the neurobiologist Bruce McEwen at Rockefeller University, extends this insight. Allostatic load is a measure of the cumulative wear-and-tear on the body from repeatedly activating the stress response beyond its natural design. High allostatic load predicts a range of later-life health problems: cardiovascular disease, Type 2 diabetes, cognitive decline, depression, accelerated ageing at the cellular level. The body can handle acute stress well; it handles chronic low-grade stress poorly.
The mindset reframe
A more recent — and more contested — line of research comes from the American psychologist Kelly McGonigal at Stanford, whose book The Upside of Stress argued that how you think about stress may matter as much as the stress itself.
McGonigal drew on work by the Harvard researcher Alia Crum and others, whose experiments suggested that people who viewed stress as a positive, energising response performed better, felt better, and showed different physiological responses than people who viewed stress as harmful. In one study, participants given a brief educational intervention about the useful purposes of the stress response — racing heart delivers more oxygen to the brain, fast breathing sharpens cognition, nervous energy fuels performance — reported reduced anxiety and showed physiological markers suggesting less taxing cardiovascular activation under the same level of stress.
This reframe has been popular, and in the right contexts it probably captures something real. How you interpret a bodily state can affect what that state does to you. Treating every jittery feeling before a presentation as evidence that you’re about to fail amplifies the response; treating it as evidence that your body is mobilising for a challenge may actually change the physiology.
That said, the research has been critiqued. Some follow-up studies have failed to replicate the strongest findings. The effect, when it exists, appears to be modest. And the popular version of the reframe — “stress is whatever you make of it” — can be harmful if it slides into dismissing genuinely damaging chronic stress as merely a mindset problem. Telling someone in a chronically abusive relationship, or a worker in a systemically overloaded job, that they should reframe their stress is at best unhelpful and at worst cruel. Mindset affects mild and moderate stress at the margins. It doesn’t fix grinding, unrelieved distress that needs structural change.
Where this leaves you
Putting the research together, a reasonably honest picture of stress looks like this.
Acute stress is fine, and often useful. The nervousness before a speech, the pressure of a demanding project, the intensity of a difficult conversation — these are examples of eustress, the kind of pressure that sharpens performance and produces growth. You don’t need to eliminate these; the attempt to live without them would be both impossible and counterproductive.
Chronic stress is corrosive, and serious. Ongoing activation of the stress response, for weeks or months or years, produces measurable harm to the body. Not because anyone’s weak or failing, but because the system wasn’t built for this. The cumulative effects show up in cardiovascular disease, cognitive decline, depression, and many other conditions. If your life has been running at elevated stress for a long period, the question of how to reduce the load is a health question, not a character question.
Mindset matters, at the margins. How you interpret moderate stress — as threatening or as fuel — can shape what it does to you. But this effect is modest, and it’s no substitute for changing the situations that produce chronic distress. The most useful role of mindset research is probably for the ordinary, day-to-day nervousness of living a demanding life; it’s less useful for serious, structural stressors.
The kinds of stress matter more than the amounts. A life with significant acute stress and good recovery periods can be deeply satisfying and produce robust health. A life with low-level chronic stress and no real recovery can be grinding even without any single intense experience. The pattern — activation and recovery, pressure and release — matters more than the total hours of stress experienced.
The question that remains
Perhaps the most useful take-away from this research is a question worth sitting with. Not how much stress are you under?, which is hard to answer meaningfully. But rather: what’s the shape of your stress?
Does it spike and subside, giving your body and mind real periods of recovery? Or does it hum along in the background, rarely resolving, so that you’ve forgotten what a truly restful state feels like? Do the stressors in your life have foreseeable ends — points at which the pressure will lift and the stress response can stand down? Or are they ongoing, with no clear horizon? Are you experiencing eustress, rising to meet genuine challenges? Or are you in distress, locked in situations you can’t affect?
The honest answers to those questions may point to parts of your life that need structural change rather than more stress-management techniques. Meditation and breathing exercises are real and useful. They are not, on their own, going to fix a chronically over-demanding job, an unreliable relationship, or ongoing financial precariousness. The stress will continue to take its toll for as long as the conditions producing it continue.
The question to carry:
Is the stress in your life mostly the kind that ends — or mostly the kind that doesn’t? The difference between these two is, according to the best current research, probably more consequential for your long-term health than almost any other variable.
Key research referenced: Hans Selye’s General Adaptation Syndrome research (The Stress of Life, 1956); Robert Sapolsky, Why Zebras Don’t Get Ulcers (1994); Bruce McEwen’s work on allostatic load; Kelly McGonigal, The Upside of Stress (2015); Alia Crum’s research on stress mindset.