The claim that stress weakens immunity is both well supported and routinely overstated. Short-term stress does not suppress immune function; it mobilises it, which makes evolutionary sense for an animal about to be injured. What impairs it is stress that persists, where the hormones that mobilise resources in an emergency remain elevated for months and the tissues exposed to them adapt by responding less. The distinction is not academic. Studies that measure a single stressful episode and studies that follow carers of chronically ill relatives are examining opposite phenomena, and the popular summary collapses them into a single warning that stress makes people ill. Reviews that pool the two kinds of study report an average effect that describes neither of them.