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National Institute for Occupational Safety and Health (NIOSH) Heat Stress Explore This Topic Search Search Clear Search For Everyone About Heat Stress Workplace Recommendations Communication Resources View all Home search clear search National Institute for Occupational Safety and Health (NIOSH) Heat Stress Menu clear search For Everyone About Heat Stress Workplace Recommendations Communication Resources View All Heat Stress Heat-related Illnesses Mar. 3, 2026 Key points Workers exposed to extreme heat or work in hot environments may be at risk for experiencing heat-related illnesses. Workers and supervisors should be trained about heat-related illnesses, symptoms, and first aid. Types Outdoor and indoor workers exposed to extreme heat or work in hot environments may be at risk for experiencing heat related illnesses. Heat-related illnesses include heat stroke, heat exhaustion, rhabdomyolysis, heat syncope, heat cramps, and heat rash. Heat stroke Heat stroke is the most serious heat-related illness. It occurs when the body can no longer control its temperature: the body's temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. When heat stroke occurs, the body temperature can rise to 106°F or higher within 10 to 15 minutes. Heat stroke can cause permanent disability or death if the person does not receive emergency treatment. Symptoms Symptoms of heat stroke include: Confusion, altered mental status, slurred speech Loss of consciousness (coma) Hot, dry skin or profuse sweating Seizures Very high body temperature Fatal if treatment delayed First aid Take the following steps to treat a worker with heat stroke: Call 911 for emergency medical care. Stay with the worker until emergency medical services arrive. Move the worker to a shaded, cool area and remove outer clothing. Cool the worker quickly, using the following methods: With a cold water or ice bath, if possible Wet the skin Place cold wet cloths on the skin Soak clothing with cool water Circulate the air around the worker to speed cooling. Place cold wet cloths or ice on the head, neck, armpits, and groin; or soak the clothing with cool water. Heat exhaustion Heat exhaustion is the body's response to an excessive loss of water and salt, usually through excessive sweating. Symptoms Symptoms of heat exhaustion include: Headache Nausea Dizziness Weakness Irritability Thirst Heavy sweating Elevated body temperature Decreased urine output First aid Treat a worker who has heat exhaustion by doing the following: Take worker to a clinic or emergency room for medical evaluation and treatment. Call 911 if medical care is unavailable. Have someone stay with the worker until help arrives. Remove the worker from the hot area and give liquids to drink. Remove unnecessary clothing, including shoes and socks. Cool the worker with cold compresses or have the worker wash their head, face, and neck with cold water. Encourage frequent sips of cool water. Rhabdomyolysis Rhabdomyolysis (rhabdo) is a medical condition associated with heat stress and prolonged physical exertion. Rhabdo causes the rapid breakdown, rupture, and death of muscle. When muscle tissue dies, electrolytes and large proteins are released into the bloodstream. This can cause irregular heart rhythms, seizures, and damage to the kidneys. Symptoms Symptoms of rhabdo include: Muscle cramps/pain Abnormally dark (tea or cola-colored) urine Weakness Exercise intolerance Asymptomatic First aid Workers with symptoms of rhabdo should: Stop activity Drink more liquids (water preferred) Seek immediate care at the nearest medical facility. Ask to be checked for rhabdomyolysis (i.e., blood sample analyzed for creatine kinase). Heat syncope Heat syncope is a fainting (syncope) episode or dizziness that usually occurs when standing for too long or suddenly standing up after sitting or lying. Factors that may contribute to heat syncope include dehydration and lack of acclimatization. Symptoms Symptoms of heat syncope include: Fainting (short duration) Dizziness Light-headedness from standing too long or suddenly rising from a sitting or lying position First aid Workers with heat syncope should: Sit or lie down in a cool place. Slowly drink water, clear juice, or a sports drink Heat cramps Heat cramps usually affect workers who sweat a lot during strenuous activity. This sweating depletes the body's salt and moisture levels. Low salt levels in muscles cause painful cramps. Heat cramps may also be a symptom of heat exhaustion. Symptoms Muscle cramps Pain or spasms in the abdomen, arms, or legs First aid Workers with heat cramps should do the following: Drink water and have a snack or a drink that replaces carbohydrates and electrolytes (such as sports drinks) every 15 to 20 minutes. Avoid salt tablets. Get medical help if the worker: Has heart problems. Is on a low sodium diet. Has cramps that do not subside within 1 hour Heat rash Heat rash is a skin irritation caused by excessive sweating during hot, humid weather. Symptoms Symptoms of heat rash include: Red clusters of pimples or small blisters Usually appears on the neck, upper chest, groin, under the breasts, and in elbow creases First aid Workers who have heat rash should: Work in a cooler, less humid environment, if possible. Keep the rash area dry. Apply powder to increase comfort. Don't use ointments and cream On This Page Types Heat stroke Heat exhaustion Rhabdomyolysis Heat syncope Heat cramps Heat rash Mar. 3, 2026 Sources Print Share Facebook LinkedIn Twitter Syndicate Content Source: National Institute for Occupational Safety and Health NIOSH The Occupational Safety and Health Act of 1970 established NIOSH as a research agency focused on the study of worker safety and health, and empowering employers and workers to create safe and healthy workplaces. 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