Heat stress vs heat exhaustion vs heat stroke
Heat stress is the total heat load from weather, work and clothing. Heat exhaustion is an illness it can cause, with heavy sweating, headache, nausea, dizziness and weakness. Heat stroke is a medical emergency: the body's temperature control fails, core temperature can exceed 106°F, and confusion, slurred speech, seizures or collapse follow. Suspected heat stroke means calling 911 and cooling the person immediately.
What is heat stress?
Heat stress is not an illness but a load. It is the combined heat the body must handle from air temperature, humidity, sun, hot surfaces, physical work and clothing. NIOSH's criteria document on occupational heat treats heat stress as the exposure and heat strain as the body's response to it.
The body copes by sending blood to the skin and sweating. When the load outpaces those defenses, stored heat rises and heat-related illness becomes possible. Humidity, heavy work and impermeable clothing all make that more likely because they limit sweat evaporation.
What are the signs of heat exhaustion?
NIOSH lists headache, nausea, dizziness, weakness, irritability, thirst, heavy sweating, elevated body temperature and decreased urine output as signs of heat exhaustion. The person is usually still alert and able to talk sensibly.
NIOSH first aid for heat exhaustion: move the person out of the heat, give cool liquids to drink in frequent sips, remove unnecessary clothing, apply cold compresses to the head and neck, and take them to a clinic or emergency room for evaluation. Heat exhaustion can progress to heat stroke if the person keeps working or stays in the heat.
What are the signs of heat stroke?
Heat stroke is the most serious heat-related illness. NIOSH defines it as an acute medical emergency caused by an excessive rise in body temperature, above 41.1°C (106°F), and failure of the body's temperature-regulating mechanism.
Warning signs include confusion, altered mental status, slurred speech, loss of consciousness, seizures, and hot, dry skin or profuse sweating. NIOSH notes body temperature can reach 106°F or higher within 10 to 15 minutes. A change in mental state is the key red flag that separates heat stroke from heat exhaustion.
Heavy sweating does not rule out heat stroke. Workers doing hard physical labor can still be sweating profusely when heat stroke begins.
How do heat stress, heat exhaustion and heat stroke compare?
| Heat stress | Heat exhaustion | Heat stroke | |
|---|---|---|---|
| What it is | The heat load on the body | Illness from fluid and salt loss and heat strain | Failure of temperature control; emergency |
| Mental state | Normal | Usually alert; may be irritable | Confused, slurred speech, seizures or unconscious |
| Skin | Warm, sweating | Heavy sweating | Hot, dry skin or profuse sweating |
| Body temperature | Normal to mildly raised | Elevated | Can exceed 106°F (41.1°C) |
| What to do | Water, rest, shade, cooling | Leave the heat, cool, sip fluids, get evaluated | Call 911, cool rapidly, stay with the person |
What should you do for suspected heat stroke?
NIOSH's first aid steps are direct:
Call 911 immediately.
Stay with the person until help arrives.
Move them to a shaded, cool area and remove outer clothing.
Cool them quickly with an ice bath if available, or wet the skin and clothing with cold water, or use cold wet cloths.
Place cold compresses or ice on the head, neck, armpits and groin, and circulate air around the person.
What other heat-related illnesses should you know?
NIOSH describes several other conditions. Heat cramps cause muscle pain or spasms in the abdomen, arms or legs; drinking water and eating a snack or electrolyte drink every 15 to 20 minutes is advised, with medical help if cramps last more than an hour. Heat syncope is fainting or lightheadedness from standing too long or rising suddenly in the heat.
Heat rash appears as red clusters of pimples or small blisters, often on the neck, chest, groin and skin folds. Rhabdomyolysis, a breakdown of muscle tissue linked to heat and exertion, can cause muscle pain, weakness and dark, tea or cola colored urine, and needs prompt medical care.
Who is most at risk of heat illness?
Risk rises with anything that adds heat or blocks heat loss: hard physical work, humid air, direct sun, and heavy or impermeable protective clothing. People who are not yet acclimatized are especially vulnerable, which is why NIOSH advises new workers to start at no more than 20% of a normal heat exposure on day 1 and increase by no more than 20% each day.
Personal factors matter too, including dehydration, recent illness, some medications and chronic health conditions. Supervisors and coworkers should watch each other, because a person developing heat stroke may not recognize their own confusion.
How do you prevent heat illness?
OSHA summarizes prevention as water, rest and shade. NIOSH recommends drinking 1 cup (8 oz.) of water every 15 to 20 minutes during moderate work lasting under 2 hours, rest in cool areas, and gradual acclimatization for new and returning workers. Cooling vests can add comfort and reduce heat strain, especially under protective clothing.
This page is educational and not a substitute for medical advice. Talk to a clinician about symptoms, medications that affect heat tolerance, or any episode of heat illness.
Key takeaways
Heat stress is the load; heat exhaustion and heat stroke are illnesses it can cause.
Confusion, slurred speech, seizures or collapse in the heat point to heat stroke, an emergency.
NIOSH defines heat stroke by core temperature above 106°F (41.1°C) with failed temperature control.
For suspected heat stroke, call 911 and cool the person rapidly while waiting.
Water, rest, shade and acclimatization are the foundation of prevention.
Frequently asked questions
What is the main difference between heat exhaustion and heat stroke?
Mental state. A person with heat exhaustion is usually alert, while heat stroke brings confusion, slurred speech, seizures or loss of consciousness as the body's temperature control fails. Heat stroke is a 911 emergency.
Can heat exhaustion turn into heat stroke?
Yes, if the person keeps working or stays in the heat. Stopping activity, cooling down and getting medical evaluation at the first signs of heat exhaustion reduces that risk.
Do you stop sweating with heat stroke?
Not always. NIOSH lists either hot, dry skin or profuse sweating as signs of heat stroke, and people doing hard work can still be sweating when it begins.
How long does it take to recover from heat exhaustion?
Recovery time varies with severity and health. Anyone with heat exhaustion should be evaluated by a clinician, who can advise on rest, fluids and return to work or exercise.
What is the difference between hypothermia and heat stroke?
They are opposites. Hypothermia is a dangerous drop in core temperature from cold exposure, while heat stroke is a dangerous rise from heat. Both are emergencies that can cause confusion and collapse.
Related reading
Sources
Heat-Related Illnesses, CDC, National Institute for Occupational Safety and Health
Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (DHHS/NIOSH Publication 2016-106), CDC, National Institute for Occupational Safety and Health
Heat Stress: Workplace Recommendations, CDC, National Institute for Occupational Safety and Health
Heat Stress: Acclimatization, CDC, National Institute for Occupational Safety and Health
Heat: Overview, Occupational Safety and Health Administration
About HEATJAC. HEATJAC is a thermal architecture company founded by an anesthesiologist. We design patented garment systems that capture, conduct and broaden warmth across the body, and we publish this knowledge hub because the science of staying warm should be public. HEATJAC products are not medical devices and are not intended to diagnose, treat, cure or prevent any disease.