Both are caused by your body overheating, but one is a warning sign and the other is a life-threatening emergency. Knowing which one you're dealing with — in yourself or someone else — determines whether you need to rest in the shade or call for help immediately.
Heat exhaustion: the warning stage
Heat exhaustion happens when your body loses too much water and salt, usually through heavy sweating during physical activity or prolonged heat exposure.
Common signs:
- Heavy sweating
- Cool, pale, or clammy skin
- Fast, weak pulse
- Nausea or vomiting
- Muscle cramps
- Tiredness, dizziness, or headache
What to do: Move to a cool or shaded place, loosen clothing, sip water slowly, and apply cool, wet cloths to the skin. Rest until symptoms fully pass. If vomiting continues, symptoms last longer than an hour, or the person's condition worsens, seek medical care.
Heat stroke: a medical emergency
Heat stroke is the most severe heat-related illness. It happens when the body's temperature regulation fails completely, and internal temperature can climb above 103°F (39.4°C) rapidly.
Common signs:
- Hot, dry skin, or skin that feels clammy despite the heat
- Little to no sweating (a key difference from heat exhaustion)
- Confusion, slurred speech, or agitation
- Throbbing headache
- Rapid, strong pulse
- Loss of consciousness
What to do: Call 911 immediately. While waiting, move the person to a cooler area, remove excess clothing, and cool them as quickly as possible — cold water immersion, ice packs to the neck, armpits, and groin, or a cool wet sheet with a fan. Do not give fluids by mouth if the person is confused or unconscious.
The core difference
The clearest signal is mental state and sweating. Someone with heat exhaustion is still alert and sweating heavily. Someone with heat stroke may stop sweating, feel hot and dry to the touch, and become confused or unresponsive. When in doubt, treat it as heat stroke and call for help — the cost of overreacting is far lower than the cost of waiting too long.
Who's most at risk
Older adults, young children, people with chronic illnesses, outdoor workers, and athletes training in high heat are at the highest risk. Certain medications, including some blood pressure drugs and diuretics, can also make it harder for the body to regulate temperature. Staying properly hydrated — see our guide on how much water you should drink a day — is one of the simplest ways to lower your risk before heat becomes a problem.
Prevention is the real fix
- Drink water regularly throughout the day, even before you feel thirsty
- Avoid strenuous outdoor activity during peak heat (typically 10 a.m. to 4 p.m.)
- Wear lightweight, light-colored clothing
- Take breaks in shade or air conditioning
- Never leave anyone in a parked car, even briefly
If you're active outdoors regularly, pairing good hydration habits with the benefits of walking 30 minutes a day means picking cooler parts of the day so the activity stays a benefit, not a risk.
The takeaway
Heat exhaustion is your body's warning signal — respond to it with rest, shade, and fluids. Heat stroke is an emergency that needs immediate medical attention and rapid cooling. Learning to spot the difference, especially the shift from heavy sweating to little or no sweating alongside confusion, can make the difference in how quickly someone gets the help they need.
For more detailed guidance, the CDC's heat-related illness resources are a reliable, authoritative source to bookmark before the next heat wave.