Heat exhaustion and heat stroke are not two points on the same scale of discomfort. Heat exhaustion is serious and generally responds to cooling and rest. Heat stroke is a medical emergency with a real risk of death, and the transition between them can happen quickly.
The distinction that matters most is mental status. Someone confused, disoriented, behaving strangely, or unconscious is a heat stroke case until shown otherwise, and that requires emergency services rather than a rest in the shade. Our roundup of insulated water bottles covers carrying enough water.
Medical Disclaimer
This is general information, not medical advice, and it cannot diagnose anything. Heat stroke is a life-threatening emergency requiring immediate professional care. If you suspect it, call emergency services first and begin cooling while waiting. When uncertain which condition you are dealing with, treat it as the more serious one.
Quick Answer
Heat exhaustion presents with heavy sweating, weakness, nausea, headache, and cool clammy skin, with the person still mentally clear. Move them to shade, cool them, and give fluids. Any confusion or loss of consciousness means heat stroke and emergency services immediately.
Telling Them Apart
| Heat exhaustion | Heat stroke | |
|---|---|---|
| Mental status | Alert and oriented | Confused, disoriented, or unconscious |
| Skin | Cool, clammy, sweating | May be hot, and sweating can stop |
| Temperature | Raised but not extreme | Very high |
| Pulse | Fast and weak | Fast and strong |
| Response | Cool, rest, fluids | Emergency services immediately |
Mental status is the most reliable field indicator. Skin presentation varies and should not be relied on to rule heat stroke out.
Recognizing Heat Exhaustion
The common signs are heavy sweating, skin that feels cool and clammy to the touch, weakness or fatigue that seems disproportionate to the effort, dizziness, headache, nausea, and muscle cramps in the legs or abdomen.
Someone with heat exhaustion typically knows something is wrong and can tell you so. That clarity is the reassuring part of the picture, and it is exactly what disappears if the condition progresses.
People frequently downplay how they feel, particularly in a group where stopping feels like letting everyone else down. Anyone slowing noticeably, going quiet, or stumbling is worth checking on directly rather than waiting for them to volunteer that something is wrong.
What to Do for Heat Exhaustion
Stop and get into shade
Any shade at all, and where none exists, create some with a tarp, an emergency blanket held overhead, or simply people standing around them to block the sun.
Cool them actively
Loosen or remove any excess clothing, wet the skin with water, and fan them steadily. Evaporation is what actually does the cooling, so wetting the skin plus moving air beats either one of those on its own.
Cool water on key areas
The neck, armpits, and groin all have major blood vessels close to the surface, and cooling those areas works considerably faster than cooling elsewhere on the body.
Fluids if they are alert
Sipping water or an electrolyte drink, slowly rather than in gulps. Never give fluids to anyone confused or not fully conscious. Our roundup of electrolyte tablets covers what to carry.
When It Becomes an Emergency
Call emergency services immediately for any confusion, disorientation, slurred speech, strange behavior, seizure, or loss of consciousness. Those indicate heat stroke.
Also escalate if symptoms do not improve within roughly thirty minutes of cooling and rest, if the person cannot keep fluids down, or if they are vomiting repeatedly.
While waiting for help, keep cooling. Aggressive cooling before professional care arrives is the single most important intervention in heat stroke, and cold water immersion where safely possible is the most effective method available in the field.
Do not give anything by mouth to someone who is confused or unconscious. Our note on hiking watches covers reaching rescuers without phone signal.
Why Hikers Are Particularly Exposed
Most public guidance on heat illness is written for people working outdoors or for older adults at home during a heatwave. Hiking presents a different version of the same problem.
You are generating heat through sustained exertion rather than simply enduring ambient temperature, which means your body is fighting on two fronts. Exertional heat illness can develop in people who are young, fit, and well hydrated, which is exactly the group most likely to assume it does not apply to them.
You are also away from help. A heat stroke case in a car park is minutes from an ambulance; the same case four miles up a trail is a considerably worse situation, and evacuation takes time that matters clinically.
And the environment offers less relief than most. Exposed desert or ridge terrain provides no shade, radiant heat comes off rock as well as down from the sun, and there is often no water to cool anyone with. Our roundup of portable water bottles covers carrying enough.
Prevention on Hot Hikes
Start early and aim to finish before the hottest part of the day, which in a genuinely hot climate is the difference between a pleasant morning walk and a dangerous afternoon one.
Drink before you feel thirsty, since thirst lags behind actual fluid loss. Replacing electrolytes matters on long hot days, because drinking large volumes of plain water while sweating heavily can dilute sodium levels.
Wear light-colored loose clothing and a wide-brimmed hat, and use shade whenever it appears rather than pushing through to a planned stopping point.
Adjust the plan for conditions. A route that suits sixty degrees is a different proposition at a hundred, and turning back is always available. Our roundup of compasses for hiking covers protection.
Who Is at Higher Risk
Older adults and young children regulate body temperature less effectively than healthy adults do. Anyone with a heart condition, taking certain medications including some diuretics and antihistamines, or who has had a previous heat illness carries meaningfully elevated risk.
People new to a hot climate are more vulnerable than those acclimatized to it, and acclimatization takes days to weeks rather than hours.
Alcohol the night before and inadequate sleep both increase risk, and neither is obvious in the moment. Anyone in a higher-risk group should discuss hot-weather activity with their doctor rather than relying on general advice.
Heat Illness FAQ
How do I tell heat exhaustion from heat stroke?
Mental status is the most reliable field indicator. Someone alert and able to tell you what is wrong is likely heat exhaustion; confusion, disorientation, strange behavior, or unconsciousness means heat stroke and emergency services immediately.
Is skin always dry in heat stroke?
No, and this is a common and dangerous misconception. Sweating can continue in heat stroke, particularly the exertional type that affects hikers. Never rule it out because someone is still sweating.
What is the fastest way to cool someone?
Wetting the skin and creating airflow, since evaporation does the work. Cold water on the neck, armpits, and groin helps, and immersion in cold water is the most effective method where it can be done safely.
Should I give them water?
Only if they are fully alert and able to swallow, sipping slowly rather than gulping. Never give fluids to anyone confused, drowsy, or unconscious, because of the risk of choking.
How long before I call for help?
Immediately for any confusion or loss of consciousness. For heat exhaustion, if symptoms are not improving within about thirty minutes of cooling and rest, or if they cannot keep fluids down, escalate rather than waiting.
Can I just drink more water to prevent it?
Water alone is not enough on long hot days. Heavy sweating loses sodium as well as fluid, and drinking large volumes of plain water can dilute it further. Electrolyte replacement matters alongside hydration.
Does acclimatization help?
Considerably, and it takes days to weeks rather than a single outing. Someone newly arrived in a hot climate is at meaningfully higher risk than a local doing the same walk.
When should I see a doctor?
Anyone who has had heat stroke needs emergency care without exception. For heat exhaustion, see a doctor if symptoms persist, recur, or were severe, and discuss hot-weather activity in advance if you have a heart condition or take medications affecting heat regulation.
Sources
- Centers for Disease Control and Prevention. Heat stress and heat-related illness. https://www.cdc.gov/niosh/topics/heatstress/
- National Weather Service. Heat safety and heat illness. https://www.weather.gov/safety/heat-illness
- Occupational Safety and Health Administration. Heat illness prevention. https://www.osha.gov/heat
Recommended Reading
See our note on what to do if you get lost.
