Heat exhaustion improves quickly when you cool down and rehydrate, but acting fast matters. Left untreated, it can progress to heat stroke, a medical emergency. Most people recover within one to two days with proper care, and the immediate steps you take in the first few minutes make the biggest difference.
What Happens in Your Body
When you overheat, your body sends a surge of blood to the skin’s surface to release heat. The veins near the skin dilate fully, and blood pools in these expanded vessels, especially in your legs. This pooling means less blood returns to your heart, which reduces cardiac output and makes your cardiovascular system work much harder to keep up.
At the same time, heavy sweating pulls large volumes of water and electrolytes out of your bloodstream. The combination of peripheral blood pooling and shrinking plasma volume is what produces the classic symptoms: heavy sweating, nausea, dizziness, headache, cool or clammy skin, a rapid weak pulse, and muscle cramps. Your body is still trying to cool itself (unlike heat stroke, where that mechanism fails), but it’s running out of resources to do so.
Immediate First Aid Steps
Speed is everything. As soon as you recognize the symptoms, take these steps:
- Get out of the heat. Move to an air-conditioned space if possible, or at least into shade. Simply moving to a cooler environment without any other intervention lowers core temperature at only about 0.05°C per minute, so passive cooling alone is slow. It’s a necessary first step, not a sufficient one.
- Lie down and elevate the legs slightly. This counters the blood pooling in dilated leg veins and helps restore blood flow to the heart and brain.
- Remove excess clothing. Tight or heavy layers trap heat. Take off shoes, socks, and any gear that isn’t necessary.
- Start active cooling. Spray or sponge the skin with cool water while fanning. This mimics your body’s evaporative cooling system but accelerates it. If you have access to a tub, bathtub, or even a large container, cool water immersion is the fastest method available.
- Begin rehydrating. Offer cool water in frequent small sips. Sports drinks are a good choice because they replace both fluid and the sodium and potassium lost through sweat. Avoid coffee, alcohol, and caffeinated sodas, which can worsen dehydration.
Which Cooling Methods Work Best
Not all cooling techniques are equal. A large review by the International Liaison Committee on Resuscitation found that water immersion techniques (sitting in cool or cold water) produce faster cooling rates than any other method, including ice packs, cold showers, wet towels, cooling vests, or evaporative cooling with fans. If you’re at home or near a facility with a bathtub, filling it with cool water and getting the person in is the single most effective thing you can do.
When immersion isn’t practical, the combination of wetting the skin and fanning is your best alternative. Placing cold packs or ice wrapped in cloth on the neck, armpits, and groin (where large blood vessels sit close to the surface) may help, though studies show limited advantage over simpler methods. Cooling vests, ice sheets, and hand-cooling devices showed no clear benefit over basic approaches in the available research.
What and How Much to Drink
Water is fine for mild cases, but if the person has been sweating heavily for an extended period, a sports drink or oral rehydration solution does a better job of replacing lost electrolytes. The goal is steady intake in small amounts. Gulping large volumes at once can trigger nausea or vomiting, which makes dehydration worse.
If the person can’t keep fluids down, is confused, has an irregular heartbeat, or doesn’t improve after 15 to 20 minutes of cooling and rehydration, that’s a sign they need emergency medical care. At that point, intravenous fluids may be necessary to restore blood volume, something that can’t be done at home.
When Heat Exhaustion Becomes Heat Stroke
The critical line between heat exhaustion and heat stroke is mental status. Someone with heat exhaustion feels awful but remains alert and oriented. Heat stroke shows up as confusion, slurred speech, loss of consciousness, or seizures, often with a core body temperature above 104°F (40°C). The skin may become hot and dry because the sweating mechanism has failed.
If you see any mental status changes, call 911 immediately and continue aggressive cooling while waiting. Heat stroke can cause organ damage and is fatal without rapid treatment. Don’t wait to see if symptoms improve on their own.
Recovery and Returning to Activity
Most people feel significantly better within an hour of starting cooling and rehydration, but full recovery takes longer than most expect. Plan on at least one to two days of rest before you feel normal again. You should wait a minimum of 48 hours before returning to physical activity or heat exposure, even if you feel fine sooner. Your body’s thermoregulatory system remains vulnerable during this window, and pushing too early invites a repeat episode.
During recovery, stay in a cool environment, keep drinking fluids, eat foods with electrolytes (fruits, broth, lightly salted snacks), and monitor for any return of symptoms. If dizziness, nausea, or headache comes back, you’re not ready to resume activity.
Medications That Raise Your Risk
Certain medications interfere with your body’s ability to cool itself, making heat exhaustion more likely and harder to recover from. According to the CDC, the main categories include:
- Beta blockers (commonly prescribed for high blood pressure and heart conditions) reduce your body’s ability to dilate skin blood vessels and can decrease sweating.
- Antipsychotics impair both sweating and the brain’s temperature regulation.
- Antidepressants affect sweating in different ways depending on the type. SSRIs and SNRIs can cause excessive sweating that accelerates fluid loss, while tricyclic antidepressants reduce sweating, trapping heat.
- Antihistamines with anticholinergic properties (like diphenhydramine, the active ingredient in Benadryl) decrease sweating and impair thermoregulation.
- Stimulant medications used for ADHD can raise body temperature directly.
- Some anti-seizure medications reduce sweating.
- Alcohol impairs your ability to perceive heat and increases sweating.
If you take any of these, you don’t necessarily need to stop them in summer, but you do need to be more cautious about hydration, shade, and recognizing early symptoms. Talk to your prescriber about a heat safety plan if you work or exercise outdoors.
Preventing a Repeat Episode
Once you’ve had heat exhaustion, you’re more susceptible to it happening again, especially in the days immediately following. Beyond the 48-hour rest period, build back into heat exposure gradually. Drink before you feel thirsty, since thirst is a lagging indicator of dehydration. Wear lightweight, loose-fitting, light-colored clothing. Schedule strenuous outdoor activity for early morning or evening when temperatures are lower. And pay attention to the heat index, not just the temperature, because humidity dramatically slows your body’s ability to cool through sweat evaporation.