The difference between useful stress and the kind that breaks you

Not all stress is the same

In 1908, psychologists Robert Yerkes and John Dodson demonstrated that there is an optimal level of arousal for performing most tasks — too little, and you are unmotivated and unfocused; too much, and performance degrades. This relationship, now known as the Yerkes-Dodson law, is one of the most widely cited ideas in psychology — though it is worth knowing that the original work was done on mice, and the inverted-U does not hold equally across every type of task. It tells us something important: stress, in the right amount, is not a problem to be eliminated. It is a feature of any situation you care about.

The physiological state of stress — the release of adrenaline and cortisol, the heightened alertness, the narrowed focus — evolved for exactly this purpose. It helps you respond to demands that matter. A deadline, a difficult conversation, a high-stakes presentation: these benefit from some degree of activation. The person who feels nothing before a job interview is not relaxed — they are either extraordinarily experienced or, more likely, not engaged enough to perform at their best.

Eustress and distress

Endocrinologist Hans Selye distinguished in the 1970s between eustress — stress that is experienced as positive, motivating, and manageable — and distress, which is experienced as overwhelming, draining, and outside your ability to cope. The physiological response is similar in both cases: the same hormones are released. The difference is primarily in the appraisal — how you interpret what is happening and whether you believe you have the resources to handle it.

This distinction matters because it shifts the target. The aim is not to reduce arousal indiscriminately. It is to manage your appraisal of events and to build genuine capacity to cope — so that situations that currently tip into distress can be handled within the eustress zone instead.

When stress becomes chronic — and why it is different

Acute stress — a spike in response to a specific demand — is what the stress system was designed for. It is time-limited. The threat passes, cortisol levels drop, the body recovers. Chronic stress is what happens when the system stays activated without recovery. The threat is not a discrete event but a persistent condition: a hostile work environment, financial insecurity, relationship conflict, a caring responsibility without end.

Chronic activation of the HPA axis (the hypothalamic-pituitary-adrenal system that runs the stress response) has documented downstream effects: disrupted sleep, impaired immune function, elevated inflammation, reduced cognitive performance, and — over long periods — increased risk of cardiovascular disease and depression. These are not hypothetical. Chronic stress is one of the most significant modifiable risk factors for a range of serious health outcomes.

The distinction between acute and chronic is clinically important because the tools that help with each are different. Managing a specific high-pressure situation is a different task from changing the structural conditions that keep your stress system chronically active. This course addresses both.

Where anxiety fits

Anxiety and stress are related but distinct. Stress is typically a response to an external demand — something is pressing on you from outside. Anxiety is characterised by apprehension about future threats — often ones that are uncertain, exaggerated, or not currently present. In practice they often co-occur, and the physiological signatures overlap. For this course, we treat them together where the tools apply to both, and separately where they diverge — particularly around cognitive patterns, which matter more for anxiety than for situational stress.