The threshold shifts, and by more than people expect
Heat guidance is written for a reference adult: middle-aged, healthy, hydrated, acclimatised, capable of a normal sweating response. Almost none of that holds automatically at 80.
The changes are physiological rather than a matter of resilience:
- Sweating starts later and produces less. The main cooling mechanism engages at a higher core temperature and runs at a lower rate.
- Thirst is unreliable. Dehydration develops without the signal that would prompt drinking.
- The heart has less reserve. Cooling requires shifting blood to the skin, and that is cardiac work.
- Kidney function declines, so fluid and electrolyte balance is harder to maintain over consecutive days.
The practical translation: read the heat index bands one step stricter. Conditions in Caution deserve the attention Extreme Caution would get for a younger adult, and the Danger band is a serious situation rather than an uncomfortable one.
Medications and conditions that lower it further
| Factor | Effect on heat tolerance |
|---|---|
| Diuretics | Increased fluid loss on top of sweating |
| Beta blockers | Blunt the heart-rate response that cooling depends on |
| Anticholinergics, some antihistamines | Reduce sweating directly |
| Antipsychotics | Can impair central temperature regulation |
| Heart failure, kidney disease, diabetes | Reduce the reserve every mechanism above draws on |
| Dementia | Reduces recognition of heat and the ability to act on it |
| Living without air conditioning | Removes the recovery period entirely during a multi-day event |
The overnight number
For this group, the afternoon peak is not the most important figure. The overnight minimum is.
A body tolerates a hot day considerably better when the following night lets core temperature and cardiovascular load return to baseline. During a multi-day event, especially a heat dome, nights stop falling — and it is those events that show up in excess mortality figures, with deaths concentrated in the later days rather than the first.
So the question to ask about a relative's home is not "is it hot in there this afternoon" but "did it cool down last night".
What to actually do
- Call, and listen rather than ask. "Are you managing?" gets a yes. Confusion, vagueness, unusual drowsiness or slurring is the signal, and it is never volunteered.
- Get one room genuinely cool and make it the room they sleep in. One cooled room beats a whole house at 30°C.
- Set drinking on a schedule, not on thirst. Small amounts often.
- Cool the skin. A damp cloth on the neck and forearms, a cool shower, feet in cool water. Effective and immediate.
- Close up during the day, open up at night — curtains and windows shut against the sun in the afternoon, opened once the outside air is genuinely cooler.
- Know the emergency line. Confusion, slurred speech, unsteadiness or collapse in the heat is treated as heat stroke: call emergency services.
Why this page exists
Most heat content is aimed at workers and athletes, because that is where the dramatic cases are. But the mortality is concentrated here — in older people, often living alone, often indoors, during multi-day events. The useful intervention is not a warning to them; it is a phone call from someone who noticed the forecast.