How to identify the three levels of heat illness, what distinguishes heat exhaustion from heat stroke, and the correct treatment for each.
Heat illness exists on a spectrum from uncomfortable (heat cramps) to fatal (heat stroke). The progression along this spectrum can be rapid — particularly in children, older adults, and people with underlying health conditions. Recognising where on the spectrum a person is, and responding appropriately to each level, is the difference between a minor incident and a preventable death.
The key distinction — between heat exhaustion and heat stroke — determines whether the situation requires immediate emergency services. Missing heat stroke and treating it as mere heat exhaustion has killed people.
| Level | Core Temperature | Mental Status | Skin | Sweating |
|---|---|---|---|---|
| Heat cramps | Normal | Normal | Normal | Yes |
| Heat syncope (faint) | Normal / slight rise | Brief loss of consciousness | Pale | Yes |
| Heat exhaustion | < 40°C (104°F) | Normal but may be anxious/confused | Pale, cool, clammy | Yes, heavy |
| Heat stroke | > 40°C (104°F) | Confused, disoriented, unconscious | Hot, red, possibly dry | May cease |
The transition from heat exhaustion to heat stroke can happen quickly, particularly in:
Heat cramps are painful muscle spasms — typically in the legs, abdomen, or arms — caused by electrolyte loss through sweating during strenuous exercise or heat exposure.
Management:
Heat cramps are not dangerous in themselves but are a sign of significant electrolyte and fluid loss. They may indicate early stages of more serious heat illness if other symptoms develop.
Heat exhaustion is the most common heat illness. It is caused by sustained exposure to high temperatures with inadequate fluid and electrolyte replacement, leading to dehydration and mild cardiovascular stress.
Signs:
The person is conscious and knows where they are.
Management:
Recovery from heat exhaustion typically occurs within 30 minutes with adequate cooling and hydration. A person who has had heat exhaustion should not return to exertion for at least 24 hours.
Heat stroke is a medical emergency. It is distinguished from heat exhaustion by neurological involvement — confusion, altered consciousness, or unconsciousness — combined with a core temperature above 40°C.
⚠️ Heat stroke is a medical emergency that can cause brain damage and death within minutes if not treated immediately. The core sign is neurological dysfunction — confusion, bizarre behaviour, loss of consciousness — in the context of heat exposure. Call 999 immediately and begin aggressive cooling while waiting.
Two types:
Signs of heat stroke:
Signs that distinguish heat stroke from heat exhaustion:
Management — Heat Stroke:
The goal is to reduce core temperature below 39°C within 30 minutes. Rapid cooling is the treatment — everything else is supportive.
| Measure | Benefit |
|---|---|
| Hydrate before activity | Starts exercise with adequate fluid |
| Regular fluid intake during heat | Replaces sweat losses; does not wait for thirst |
| Electrolyte replacement | Sports drinks, bananas, salted snacks for prolonged activity |
| Shade and cool resting periods | Reduces heat load |
| Acclimatisation | 10–14 days of gradual heat exposure before strenuous activity |
| Cool environment during heat waves | Particularly for elderly; air conditioning access |
| Check on vulnerable people | During heat waves, regular welfare checks on elderly neighbours |
| Level | Key Sign | Treatment |
|---|---|---|
| Heat cramps | Muscle spasm; normal mental status | Rest; cool area; oral fluids with electrolytes |
| Heat exhaustion | Pale, sweaty; dizzy; conscious and oriented | Cool environment; cooling measures; oral fluids; monitor |
| Heat stroke | Confused or unconscious + hot | Call 999; aggressive cooling immediately; ice packs to neck/armpits/groin |
| Heat stroke vs. exhaustion | Mental status is key distinction | If confused: treat as heat stroke |
| Temperature > 40°C | Heat stroke territory | Emergency |
| Cooling target | Below 39°C | Stop cooling at 39°C to avoid overcooling |
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