On a hot summer day, your body works hard to keep itself cool — and most of the time, it succeeds. But when the heat overwhelms that cooling system, things can go wrong fast. Heat illness exists on a spectrum, and two stages get confused all the time: heat exhaustion and heat stroke. They sound similar, but the difference between them is the difference between "rest in the shade and you'll be fine" and "call an ambulance right now."
Knowing which one you're looking at — in yourself, a child, a coworker, or an older relative — can save a life. Here's how to tell them apart, and exactly what to do for each.
Your body likes to sit right around 98.6°F (37°C). When you get too hot, it cools itself mainly by sweating — sweat evaporates off your skin and carries heat away. To help, your heart pumps more blood toward the skin, which is why you flush red on a hot day.
This system has limits. If it's extremely hot, or very humid so sweat can't evaporate, or you're exercising and losing fluid faster than you replace it, your core temperature starts to climb. High humidity is the silent multiplier here — it's the same reason the heat index can make 95°F (35°C) feel like 110°F (43°C). When the cooling system falls behind, heat illness begins.
Heat exhaustion is your body waving a red flag. It happens when you've lost a lot of water and salt through heavy sweating and your core temperature is elevated — but your body's emergency thermostat is still working. Core temperature is typically between 100°F and 104°F (38°C to 40°C).
The telltale signs of heat exhaustion:
• Heavy sweating — often drenching, with cool, pale, clammy skin
• Weakness and fatigue — you feel drained and shaky
• Dizziness or lightheadedness, sometimes fainting
• Nausea or vomiting
• Headache
• Muscle cramps
• A fast, weak pulse
The key reassuring sign is that the person is still sweating and is mentally clear — confused or "off," maybe, but able to talk to you and answer questions. Heat exhaustion is serious, but it's manageable if you act.
Heat stroke is what happens when the cooling system fails completely. The body can no longer regulate its temperature, and the core climbs to 104°F (40°C) or higher. At that point, the heat starts to damage the brain, heart, kidneys, and muscles. It is a life-threatening medical emergency, and every minute counts.
The warning signs that separate heat stroke from heat exhaustion:
• Confusion, slurred speech, agitation, or delirium — the most important sign
• Loss of consciousness or seizures
• Very high body temperature — 104°F (40°C) or above
• Hot, red skin that is often dry — in classic heat stroke the person may have stopped sweating, though in exertional heat stroke they can still be sweaty
• A rapid, strong pulse
• Throbbing headache, nausea
Do not wait to see whether it improves. If you suspect heat stroke, call emergency services immediately.
| Sign | Heat Exhaustion | Heat Stroke |
|---|---|---|
| Mental state | Alert, maybe tired | Confused, slurred, unconscious |
| Core temperature | Up to 104°F (40°C) | 104°F (40°C) and above |
| Skin | Cool, pale, clammy | Hot, red — often dry |
| Sweating | Heavy | May have stopped |
| Pulse | Fast, weak | Fast, strong |
| Severity | Serious — act now | Life-threatening emergency |
The goal is simple: cool the person down and rehydrate them before it escalates.
1. Move to a cooler place — shade, an air-conditioned room, or at least out of direct sun.
2. Lie down and loosen clothing. Elevate the legs slightly if they feel faint.
3. Sip cool water or a sports drink with electrolytes. Avoid alcohol and caffeine.
4. Cool the skin — apply cool, wet cloths, mist with water, or take a cool shower.
5. Rest. Don't return to activity until you feel fully recovered.
Symptoms should ease within 30–60 minutes. If they don't improve in an hour, or get worse, or the person starts vomiting or acting confused, treat it as heat stroke and call for help.
1. Call 911 (or your local emergency number) immediately.
2. Move the person to a cooler place right away.
3. Cool them as fast as possible while you wait for help: get them into cool water if you can, or drench them with cool water and fan them, and place ice packs at the neck, armpits, and groin where large blood vessels run close to the skin.
4. Do not give fluids to anyone who is confused or unconscious — they could choke.
5. Stay with them and monitor breathing until help arrives.
Rapid cooling is the single most important treatment. Every minute the core stays above 104°F (40°C) increases the risk of lasting harm.
Heat illness can strike anyone, but some people are far more vulnerable. Infants and young children, adults over 65, people with chronic illnesses like heart disease or diabetes, and those taking certain medications all have a harder time regulating temperature. Outdoor workers and athletes are at risk from exertion, and anyone without access to air conditioning during a prolonged hot spell — like a heat dome — faces compounding danger as the heat builds day after day. Cities make it worse, too, because the urban heat island effect keeps neighborhoods dangerously warm overnight.
The best emergency is the one that never happens. On hot days, drink water steadily before you feel thirsty, take frequent breaks in the shade or air conditioning, and avoid strenuous activity during the hottest hours — usually late morning through mid-afternoon. Wear light, loose, light-colored clothing, and never leave children or pets in a parked car, where temperatures can climb 20°F (11°C) in just ten minutes. Checking the heat index before you head out tells you how hard your body will actually have to work.
Heat exhaustion and heat stroke are two points on the same dangerous path. Heat exhaustion means cool, pale, sweaty skin and a clear mind — get into the shade, hydrate, and rest, and you'll recover. Heat stroke means hot skin and a confused mind — and it's a 911 emergency that demands immediate, aggressive cooling. When in doubt, the mental-clarity test is your guide: if the person isn't thinking straight, don't wait. Stay hydrated, respect the heat, and check the forecast before you head out into a hot day.
→ Check the "feels like" temperature in your area on ClearCast