Heat Exhaustion vs Heat Stroke: How to Tell the Difference and What to Do Right Away
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Quick answer: heat stroke is a life-threatening emergency, and the CDC lists its signs as a body temperature of 103°F or higher, hot red skin that may be dry or damp, a fast strong pulse, headache, dizziness, nausea, confusion and losing consciousness. Call 911, move the person somewhere cooler and cool them with cool cloths or a cool bath, and do not give them anything to drink. Heat exhaustion usually brings heavy sweating, cold pale clammy skin, a fast weak pulse, nausea, cramps, weakness and fainting. Move to a cool place, loosen clothing, use cool wet cloths and sip water, and get medical help if the person vomits, symptoms worsen or they last longer than an hour.
The National Weather Service ranks heat among the leading weather-related causes of death in the United States, and cities can be especially dangerous. Pavement and buildings absorb heat during the day and release it at night, so neighborhoods may not cool off enough for bodies to recover. During a heat wave, knowing the difference between heat exhaustion and heat stroke can help you act quickly for yourself, a neighbor or a family member.
This guide is based on guidance from the Centers for Disease Control and Prevention (CDC), the National Weather Service (NWS) and Ready.gov. It is part of our severe weather preparedness guide. It is general information, not medical advice. In an emergency, call 911.
Sources: Centers for Disease Control and Prevention, “Heat-Related Illnesses” warning signs and first aid chart and extreme heat guidance for high-risk groups; National Weather Service, HeatRisk tool, heat index information and heat alert definitions; Ready.gov, Extreme Heat; National Highway Traffic Safety Administration, vehicular heatstroke prevention; American College of Sports Medicine guidance on exertional heat illness. Checked October 2026.
Heat Exhaustion vs Heat Stroke at a Glance
| Heat exhaustion | Heat stroke | |
|---|---|---|
| Body temperature | May be normal or elevated | 103°F or higher |
| Skin | Cold, pale and clammy, with heavy sweating | Hot and red, may be dry or damp |
| Pulse | Fast and weak | Fast and strong |
| Mental state | Tired, weak, dizzy, may faint | Confusion, may lose consciousness |
| Other signs | Nausea or vomiting, muscle cramps, headache | Headache, dizziness, nausea |
| What to do | Cool down, sip water, get help if it worsens or lasts over 1 hour | Call 911 immediately and cool the person |
The CDC’s chart is the basis for this table. The single biggest clue is the brain: confusion, slurred speech, strange behavior or unconsciousness during heat exposure points toward heat stroke.
Heat Stroke: A Medical Emergency
Heat stroke happens when the body can no longer control its temperature. Body temperature rises rapidly, sweating may fail, and the body cannot cool down. Without emergency treatment, heat stroke can cause permanent disability or death.
Warning signs
According to the CDC, watch for:
- High body temperature of 103°F or higher
- Hot, red, dry or damp skin
- Fast, strong pulse
- Headache and dizziness
- Nausea
- Confusion
- Losing consciousness (passing out)
What to do
The CDC’s steps for heat stroke are:
- Call 911 right away. Heat stroke is a medical emergency.
- Move the person to a cooler place, such as shade or an air-conditioned room.
- Help lower their temperature with cool cloths or a cool bath.
- Do not give them anything to drink. Someone who is confused or losing consciousness could choke.
While waiting for help, keep cooling. Fanning a person whose skin has been wet with cool water can speed cooling. Ice packs at the neck, armpits and groin are commonly recommended by first aid organizations as well. For athletes and workers who collapse from exertion, the American College of Sports Medicine emphasizes rapid whole-body cooling, ideally cold-water immersion when trained staff are present, because the faster the temperature comes down, the better the outcome.
If the person stops breathing normally, begin CPR. Our guide to hands-only CPR and AED basics covers the steps.
Heat Exhaustion: Serious, and a Warning
Heat exhaustion is the body’s response to losing too much water and salt, usually through heavy sweating. It can progress to heat stroke if it is not treated.
Warning signs
The CDC lists these signs of heat exhaustion:
- Heavy sweating
- Cold, pale and clammy skin
- Fast, weak pulse
- Nausea or vomiting
- Muscle cramps
- Tiredness or weakness
- Dizziness and headache
- Fainting (passing out)
What to do
- Move to a cool place, ideally air-conditioned.
- Loosen tight or heavy clothing.
- Put cool, wet cloths on the body or take a cool bath.
- Sip water.
Get medical help right away, according to the CDC, if the person is throwing up, symptoms get worse or symptoms last longer than 1 hour.
Heat Cramps and Other Heat Illnesses
Heat cramps are often the first sign that the body is struggling. The CDC describes them as heavy sweating during intense exercise along with muscle pain or spasms. The advice: stop physical activity and move to a cool place, drink water or a sports drink, and wait for the cramps to go away before doing more activity. Get medical help right away if cramps last longer than 1 hour, if the person is on a low-sodium diet or if they have heart problems.
Other heat-related conditions include:
- Sunburn, which is painful, red and warm skin, sometimes with blisters
- Heat rash, small red clusters of pimples or blisters, often on the neck, chest, groin or in elbow creases
Both are uncomfortable, and both are reminders to get out of the heat and sun.
Who Is Most at Risk
Anyone can develop heat illness, but the CDC identifies groups at higher risk:
- Adults 65 and older, whose bodies may not adjust as well to temperature changes
- Infants and young children, who rely on others to keep them cool and hydrated
- People with chronic medical conditions, such as heart disease, and people taking certain medications
- Outdoor workers and people doing strenuous work in heat
- Athletes, especially during practices in hot weather
- People with lower incomes, who may not have or be able to run air conditioning
- Pregnant people
In cities, older adults who live alone in apartments without air conditioning face a particular risk. Checking on them at least twice a day during a heat wave is a simple step that can save a life. Ready.gov encourages people to check on family members, older adults and neighbors during extreme heat.
Never leave anyone in a parked car
The National Highway Traffic Safety Administration warns that the temperature inside a parked car can rise quickly, even with windows cracked and on days that do not feel extremely hot. Children and pets should never be left in a vehicle, not even for a few minutes. Make a habit of checking the back seat every time you park.
Working and Exercising in the Heat
Physical effort makes the body produce more heat, which is why outdoor workers and athletes appear on every high-risk list. The Occupational Safety and Health Administration (OSHA) built its heat campaign around three words: water, rest and shade.
OSHA also stresses acclimatization, the process of gradually building tolerance to heat over several days. Workers who are new to a job, or returning after time away, have not adjusted yet, and OSHA notes that many heat-related worker deaths happen in the first few days on the job. Employers are encouraged to increase workloads gradually and watch new workers closely.
For anyone exercising or doing heavy chores on a hot day, practical steps include:
- Schedule hard effort for early morning or evening.
- Take frequent breaks in shade or air conditioning.
- Drink water regularly instead of waiting for thirst.
- Use the buddy system so someone notices if you become confused or unsteady.
- Stop immediately if you feel dizzy, faint, nauseated or develop cramps.
Medications and Heat
Some medications can change how the body handles heat. The CDC notes that certain drugs, including some used for mental health conditions, high blood pressure and heart disease, can make it harder to regulate temperature or stay hydrated. Others can increase sensitivity to the sun.
Do not stop a prescribed medication on your own. Ask a doctor or pharmacist before summer whether your prescriptions raise your heat risk and what extra precautions make sense. Keep medications stored at the temperatures listed on the label, since some can lose effectiveness when an apartment gets very hot during an outage.
Know the Forecast: Heat Index, HeatRisk and Heat Alerts
The NWS heat index combines temperature and humidity to show how hot it feels. High humidity makes it harder for sweat to evaporate, which is how the body cools itself.
The NWS also publishes HeatRisk, a color-coded forecast that estimates the risk of heat-related health impacts over the next week, from green (little to no risk) through yellow, orange and red to magenta (extreme). HeatRisk factors in how unusual the heat is for the time of year and location and whether nights stay warm.
Heat alerts from the NWS include:
- Heat Advisory, issued when dangerous heat is expected
- Extreme Heat Watch, issued when extreme heat is possible in the coming days
- Extreme Heat Warning, issued when extreme heat is expected or occurring
The NWS renamed its Excessive Heat products to Extreme Heat in 2025. Sign up for local alerts so you get warnings early; our guide to emergency alerts and local sign-ups explains the options.
Preventing Heat Illness in the City
The CDC’s prevention advice centers on three ideas: stay cool, stay hydrated and stay informed.
Stay cool
- Spend time in air conditioning. If your home does not have it, visit a library, mall or public cooling center. Many cities open cooling centers during heat waves and list locations through 311 or the city website.
- Do not rely on a fan alone. The CDC notes that electric fans may make you more comfortable but will not prevent heat-related illness when temperatures are very high.
- Take cool showers or baths.
- Wear lightweight, light-colored, loose clothing.
- Limit outdoor activity to the coolest parts of the day, usually morning and evening.
- Close blinds and curtains on sun-facing windows during the day.
Stay hydrated
- Drink more fluids, regardless of how active you are, and do not wait until you are thirsty.
- Avoid very sugary or alcoholic drinks, which can cause you to lose more body fluid.
- Ask a doctor how much to drink if you have a condition that limits fluids or take water pills.
Plan for power outages
Heat waves strain the power grid, and an outage during extreme heat removes the air conditioning you depend on. Our guide to extreme heat safety during a heat wave and power outage covers backup plans, including where to go when the power fails.
Heat Safety Kit Ideas for Apartments
A few supplies make hot days safer:
- Reusable water bottles and a supply of drinking water
- A digital thermometer to check body temperature and the temperature indoors
- Cooling towels or washcloths
- A battery-powered fan for comfort during outages
- Electrolyte drinks for heavy sweating
- Sunscreen and a wide-brimmed hat for time outdoors
- A list of nearby cooling centers and their hours
Store these alongside the rest of your small apartment first aid kit so they are easy to find.
Frequently Asked Questions
What is the main difference between heat exhaustion and heat stroke?
Heat stroke involves a body temperature of 103°F or higher and changes in mental state, such as confusion or passing out, and it requires 911. Heat exhaustion usually involves heavy sweating, clammy skin and weakness, and often improves with cooling and fluids.
Should I give water to someone with heat stroke?
No. The CDC says not to give a person with heat stroke anything to drink. Call 911 and cool them while you wait.
Can heat exhaustion turn into heat stroke?
Yes. Untreated heat exhaustion can progress to heat stroke, so cool down right away and get medical help if symptoms worsen or last more than an hour.
Is a fan enough during a heat wave?
Not when temperatures are very high. The CDC notes fans may provide comfort but will not prevent heat-related illness, so seek air conditioning.
Who should I check on during a heat wave?
Older adults, people living alone, people with chronic illnesses, infants and young children, and anyone without air conditioning.
The Bottom Line
Heat exhaustion is a warning; heat stroke is an emergency. Watch for confusion, a temperature of 103°F or higher and hot, red skin, and call 911 if you see them. Cool down early, drink fluids, find air conditioning and check on neighbors who might be at risk when the next heat wave arrives.
