Heat exhaustion is your body’s warning sign that it can no longer cool itself fast enough, usually after hours of exertion, heat and not enough fluids. It is common on hot hikes, long kayak days and any outdoor activity where you underestimate how much water and salt you are losing to sweat. Caught early, it resolves in 30 to 60 minutes with the right response. Left unaddressed, it can progress into heat stroke, which is a medical emergency. Here is how to recognize it and treat it, step by step.
This article is for general information and is not medical advice. Call emergency services immediately if someone stops sweating, becomes confused, or loses consciousness in the heat, as these are signs of heat stroke.
Recognizing heat exhaustion
Watch for a combination of: heavy sweating, cool and clammy or pale skin, a fast and weak pulse, muscle cramps, nausea or vomiting, dizziness or lightheadedness, headache, fatigue or weakness, and sometimes fainting. The person is usually still sweating heavily, alert, and able to answer questions clearly, even if they feel awful. That last point is the key thing that separates heat exhaustion from heat stroke.
Step 1: get out of the heat immediately
Move to shade, an air-conditioned space, or at minimum somewhere with airflow, right away. Stop all physical activity. If you are on a trail, this means stopping and resting, not pushing on to the next landmark. Loosen or remove excess clothing, especially anything tight or dark-colored that traps heat.
Step 2: cool the body down
- Apply cool, wet cloths to the skin, focusing on the neck, armpits, and groin, where blood vessels sit close to the surface and cooling has the biggest effect.
- Fan the person while the skin is damp; evaporation is what actually pulls heat away.
- A cool (not ice-cold) shower or bath works well if one is available nearby.
- Misting with water combined with a fan is a solid field substitute when no shower is around.
Step 3: rehydrate properly
Sip cool water slowly rather than gulping a large volume at once, which can trigger nausea or vomiting. If cramping or heavy sweating has been going on for a while, an electrolyte drink or oral rehydration solution is more effective than plain water alone, since heat exhaustion often involves salt loss as well as fluid loss. Avoid alcohol and caffeinated drinks, both of which work against rehydration. Improvement is usually noticeable within 30 minutes; if it is not, treat it as an emergency and seek medical care.
How heat exhaustion differs from heat stroke
This distinction matters because the response is different. Heat exhaustion: heavy sweating, skin is cool or clammy, person is alert and coherent, symptoms improve with cooling and fluids within an hour. Heat stroke: sweating may stop, skin can be hot, dry or flushed, body temperature above 103°F (39.4°C), confusion, slurred speech, seizures, or loss of consciousness. Heat stroke is a medical emergency; call for emergency help immediately and cool the person aggressively (cold water immersion if possible) while waiting for responders. Do not give fluids by mouth if the person is not fully alert, due to choking risk.
Why it happens on hikes and outdoor trips
Heat exhaustion is especially common on exposed trails with little shade, on humid days when sweat cannot evaporate efficiently, and during the first hot day of the season before your body has acclimated. Carrying too little water, underestimating trail difficulty, and pushing through the hottest part of the day (typically 11am to 4pm) are the most common contributing factors. Sun exposure compounds the problem; our guide to preventing sunburn and skin damage covers the sun-protection side of hot-weather hikes, and pairing that with the right gear from our hiking gear essentials guide reduces heat buildup in the first place.
Preventing heat exhaustion before it starts
- Drink before you are thirsty. Thirst lags behind actual fluid needs, especially in heat. Aim for regular small sips throughout a hot hike rather than large amounts at rest stops.
- Add electrolytes on long, sweaty days. Plain water alone will not replace lost sodium; an electrolyte tablet or mix in one bottle is a simple fix.
- Schedule around the heat. Start early morning or plan the exposed sections for late afternoon when temperatures ease.
- Wear light-colored, breathable, moisture-wicking clothing and a wide-brimmed hat to reduce direct heat absorption.
- Acclimate gradually if you are new to hot-weather activity; give your body several sessions in the heat before attempting a long, strenuous one.
- Know your own early warning signs. Everyone’s first symptom is a little different (headache, sudden fatigue, goosebumps despite the heat); learning yours means you catch it sooner next time.
Special considerations for kayaking and water sports
Heat exhaustion is easy to miss on the water because a splash of cool water on your skin can mask how hot your core is actually getting, and reflected sun off the water increases UV and heat exposure beyond what you would get on land. Take shaded breaks, hydrate on a schedule rather than waiting to feel thirsty, and if you start feeling unusually fatigued or dizzy on a paddle, get to shore and out of direct sun before it progresses. Our guide to choosing a properly fitted life jacket is worth pairing with hot-weather paddling since a poor-fitting vest adds unnecessary heat and restricts the cooling airflow you need.
When to seek medical care
Get medical help if symptoms do not improve within an hour of cooling and rehydration, if vomiting prevents keeping fluids down, if the person has a history of heart problems, or if you are unsure whether you are looking at heat exhaustion or the more dangerous heat stroke. When in doubt, treat it as the more serious condition and call for help; the cost of being overly cautious with heat illness is far lower than the cost of missing heat stroke.
Frequently Asked Questions
How long does heat exhaustion take to recover from?
With prompt cooling, rest and rehydration, most people start feeling noticeably better within 30 to 60 minutes. Full recovery, including a return to normal energy levels, can take the rest of the day. If there is no improvement within an hour, seek medical attention.
What is the fastest way to cool someone down with heat exhaustion?
Move them to shade or air conditioning, apply cool wet cloths to the neck, armpits and groin, fan the damp skin to encourage evaporation, and give small sips of cool water or an electrolyte drink. A cool shower or bath works well if one is available.
Can you get heat exhaustion even if you are drinking water?
Yes. Heat exhaustion is caused by both fluid loss and electrolyte (mainly sodium) loss through heavy sweating. Drinking plain water without replacing electrolytes on a long, hot day can still leave you vulnerable, especially during multi-hour hikes or paddles.
How do I know if it has turned into heat stroke?
Heat stroke involves confusion, slurred speech, a body temperature above 103°F, hot and often dry skin, and possible loss of consciousness or seizures. If the person is not alert, coherent and responsive, or sweating has stopped despite the heat, treat it as heat stroke and call emergency services immediately.