Heat Exhaustion vs. Heat Stroke: How to Tell Them Apart

Most people who get into trouble with heat on a tropical holiday were not doing anything reckless. They were walking to lunch, snorkelling off a boat, or waiting for a taxi with no shade. Heat illness builds quietly, and by the time it announces itself the person affected is usually the last one in the group to notice.

Heat exhaustion and heat stroke sit on the same scale. Heat exhaustion is the body struggling to cope. Heat stroke is the body's cooling system having failed outright. The first is treated with shade, rest, and fluids. The second is treated in a hospital, and delay costs lives.

Heat exhaustion vs. heat stroke, side by side

Signs of heat stroke

The single most useful thing to watch is how the person is thinking, not how they are sweating. Sweating can stop for ordinary reasons and can continue even in heat stroke. Confusion, slurred speech, aggression, stumbling, or loss of consciousness in someone who has been hot is the sign that changes everything.

Heat exhaustion symptoms

Heat exhaustion rarely arrives as one dramatic symptom. The signs of heat exhaustion turn up as several small ones at once:

• Heavy sweating with cool, pale, clammy skin
• Headache and dizziness, worse on standing up
• Nausea, sometimes vomiting
• Muscle cramps, often in the legs or abdomen
• Weakness and a heavy, drained feeling
• A fast, weak pulse
• Dark urine, or not needing to urinate

Heat exhaustion treatment: what to do

1. 1Stop. Get out of the sun and into shade or air conditioning. Continuing to push through is how heat exhaustion becomes heat stroke.
2. 2Lie down and raise the legs slightly.
3. 3Cool the skin — a cool shower, a wet towel, or a fan. Moving air over damp skin cools far faster than either alone.
4. 4Sip fluids that contain salt as well as water. Plain water alone replaces what was lost only partly, because sweat carries sodium out with it.
5. 5Do not go back out. Rest for the remainder of the day, and keep the following day light.

Skip alcohol entirely while recovering, and go easy on it the next day. It works against you on both fronts — it increases fluid loss and it blunts the judgement you need to notice the problem returning.

Heat exhaustion: how long does it last?

Treated promptly, the worst of heat exhaustion usually eases within half an hour to a couple of hours. Feeling fully normal takes longer. It is common to spend the next 24 to 48 hours tired, headachy, and unusually sensitive to heat — which is exactly the window in which people are most likely to overheat a second time, because they assume they have recovered.

If someone is not clearly improving within about an hour of being cooled and given fluids, or if they cannot keep fluids down, that is the point to seek medical help rather than wait longer.

Where IV fluids fit — and where they don't

For mild heat exhaustion in someone who is alert and able to drink, oral fluids work and nothing more is needed. The case for intravenous fluids is narrower and worth stating plainly: they matter when someone cannot keep oral fluids down, because vomiting turns drinking into a losing battle.

What IV fluids are not is a treatment for heat stroke. Heat stroke needs rapid cooling and hospital monitoring, and anyone showing its signs should be taken to a hospital rather than treated where they are.

Preventing heat exhaustion and heat stroke

Humidity is what makes tropical heat deceptive. Sweat cools you by evaporating, and in humid air it evaporates poorly — so you lose the fluid without getting the full cooling benefit. A temperature that would be manageable in a dry climate is considerably harder here.

• Drink before you are thirsty. Thirst lags behind actual fluid loss.
• Add salt back, not just water — through food or an electrolyte drink.
• Keep the hardest activity to the early morning or late afternoon.
• Wear loose, light-coloured clothing and a hat with a real brim.
• Remember that water sports hide the warning signs — you do not feel yourself sweating in the sea, and the glare doubles your sun exposure.
• Give yourself two or three easy days on arrival. Adjusting to heat takes time, and the first days of a trip are when most people overdo it.

Watch the people you are travelling with, too. Heat clouds judgement early, which means the person who most needs to stop is usually the one least able to decide it.