Heat and Cold Emergencies: First Aid for Temperature Extremes

Exposure to extreme temperatures can overwhelm the body’s thermoregulatory systems, producing a spectrum of injuries ranging from mild discomfort to death. The CDC estimates that more than 1,300 people die annually in the United States from extreme heat exposure, and hundreds more succumb to cold-related illness. Heat and cold emergencies follow predictable patterns — recognizing the early warning signs and taking prompt action can prevent progression to life-threatening stages. This guide covers heat emergencies (heat cramps, heat exhaustion, and heat stroke) and cold emergencies (hypothermia and frostbite) with evidence-based protocols from the CDC, the American Red Cross, the WHO, and the Mayo Clinic.

How the Body Regulates Temperature

The human body maintains a core temperature of approximately 37°C (98.6°F) through a balance of heat production and heat loss. The hypothalamus acts as the body’s thermostat, triggering mechanisms to shed heat (sweating, vasodilation) or conserve it (shivering, vasoconstriction). When environmental conditions overwhelm these mechanisms — high temperature and humidity, low temperature and wind, or immersion in cold water — body temperature deviates from the normal range, producing heat or cold illness.

The wet-bulb globe temperature (WBGT) index is a more accurate measure of heat stress than air temperature alone because it accounts for temperature, humidity, wind speed, and solar radiation. The American College of Sports Medicine uses WBGT to recommend activity modifications during athletic events.

Heat Emergencies: From Cramps to Heat Stroke

Heat cramps are the mildest form of heat illness. They manifest as painful, involuntary muscle spasms in the legs, arms, or abdomen after heavy exertion in heat. The exact cause is debated, but electrolyte depletion and dehydration are central contributors. The CDC recommends rest in a cool location, ingestion of electrolyte-containing fluids (sports drinks or oral rehydration solutions), and gentle stretching of the affected muscles. Cramps typically resolve within 30 to 60 minutes.

Heat exhaustion is a more significant condition resulting from volume depletion due to heavy sweating. Symptoms include heavy sweating, cool and clammy skin, weak pulse, dizziness, headache, nausea, vomiting, and mild confusion. Core body temperature may be elevated to 38.3°C to 40°C (101°F to 104°F), but the person remains conscious and oriented. The American Red Cross advises immediate treatment: move the person to a cool or air-conditioned location, remove excess clothing, apply cool wet cloths or ice packs to the neck, armpits, and groin, and encourage small sips of cool water or a sports drink if they are fully conscious and not nauseated. Most people recover within 30 to 60 minutes with appropriate treatment. If symptoms worsen or do not improve within 30 minutes, heat exhaustion may be progressing to heat stroke.

Heat stroke is a life-threatening emergency. The defining feature is central nervous system dysfunction — confusion, disorientation, slurred speech, seizures, or loss of consciousness — accompanied by a core body temperature exceeding 40°C (104°F). In classic (non-exertional) heat stroke, the skin is hot, red, and dry because the sweating mechanism has failed. In exertional heat stroke — seen in athletes, outdoor workers, and military personnel — the skin may remain moist from sweat. The distinction does not change the urgency of treatment.

Heat stroke kills and disables by triggering a systemic inflammatory response that damages the brain, liver, kidneys, heart, and muscles. The WHO emphasizes that rapid cooling is the single most important intervention. While waiting for emergency services, move the person to a shaded or air-conditioned area, remove clothing, and initiate aggressive cooling. The CDC recommends cold water immersion (1°C to 15°C / 34°F to 59°F) as the gold standard when feasible. If immersion is not possible, apply ice packs to the neck, armpits, and groin, cover the person with cold wet sheets, and use fans to enhance evaporative cooling. Stop cooling once the core temperature reaches 39°C (102.2°F) to avoid overshoot hypothermia. The AHA notes that seizure management and airway protection may be necessary.

Cold Emergencies: Hypothermia and Frostbite

Hypothermia occurs when core body temperature drops below 35°C (95°F). The WHO identifies the classic stages: mild (32°C to 35°C / 90°F to 95°F), moderate (28°C to 32°C / 82°F to 90°F), and severe (below 28°C / 82°F). The CDC reports that hypothermia kills approximately 1,500 people in the United States each year.

Mild hypothermia presents with intense shivering, cold and pale skin, mild confusion, poor coordination, and increased heart rate and blood pressure. The NIH emphasizes that shivering is the body’s attempt to generate heat — as long as shivering continues, the person has some ability to rewarm spontaneously. First aid includes moving the person indoors, removing wet clothing, and passively rewarming with blankets and dry clothing. Warm, sweet, non-alcoholic beverages can help if the person is conscious and able to swallow. Avoid alcohol, which causes vasodilation and accelerates heat loss.

Moderate hypothermia is characterized by cessation of shivering — the body has exhausted its heat-producing reserves — along with decreasing heart rate and respiratory rate, worsening confusion or irrational behavior (some people paradoxically remove clothing), dilated pupils, and drowsiness. The American Red Cross advises that handling must be extremely gentle. Rough movement can trigger ventricular fibrillation in the hypothermic heart. Passive rewarming alone is insufficient; active external rewarming is needed — warm water bottles or chemical heat packs wrapped in cloth applied to the chest, armpits, and groin. Do not immerse in hot water or use electric heating devices, which can cause burns in vasoconstricted skin.

Severe hypothermia is a critical emergency. The person may be unconscious, with undetectable pulse and minimal respiratory effort. The Mayo Clinic warns that “no one is dead until warm and dead” — severely hypothermic patients have been resuscitated after prolonged cardiac arrest. Aggressive handling can trigger cardiac arrest. Begin passive rewarming and active external rewarming. If the person is unresponsive and not breathing normally, start CPR following standard protocols. Use AED as directed; the device will analyze the rhythm and advise whether shock is indicated. Transport to an advanced cardiac life support facility capable of cardiopulmonary bypass or extracorporeal membrane oxygenation.

Frostbite results from freezing of tissue. The CDC reports that fingers, toes, nose, ears, cheeks, and chin are most commonly affected. Frostbite is classified into four degrees, but for first aid purposes, the distinction between superficial and deep frostbite is most practical.

Superficial frostbite affects the skin surface and underlying tissue. The skin appears pale, waxy, or white, and feels firm but pliable. The person may report numbness or a sensation of “clumsiness.” The American Red Cross recommends rewarming using body heat — placing frostbitten fingers in the armpits, for example. Do not rub or massage the area; ice crystals in the tissue cause cell damage when manipulated. Do not use direct heat sources — hair dryers, heating pads, or open flames — as numb tissue burns easily.

Deep frostbite extends into muscle and bone. The affected part is cold, hard, and insensate. Blisters may appear after rewarming. Field rewarming is controversial; if there is any risk of refreezing, it is safer to delay rewarming until definitive medical care is available — refreezing after thawing causes catastrophic tissue damage. When medical care is accessible, rapid rewarming in water heated to 37°C to 39°C (98.6°F to 102.2°F) for 15 to 30 minutes is the gold standard, per the CDC. Analgesics are required because rewarming is intensely painful. Blisters should be managed by medical professionals. Smoking and other vasoconstrictive activities are strictly prohibited during recovery.

Immersion Hypothermia: Special Considerations

Cold water immersion accelerates heat loss — water conducts heat approximately 25 times faster than air at the same temperature. The American Red Cross notes that the initial “cold shock” response on water entry — gasping, hyperventilation, and tachycardia — can lead to drowning within minutes. After 5 to 15 minutes, neuromuscular function declines to the point that self-rescue becomes impossible. After 30 minutes, hypothermia sets in even in moderately cold water.

If you witness someone fall into cold water, call 911 and the local water rescue service. Throw a flotation device with a line. Do not enter the water unless you are trained and equipped for water rescue. The drowning rescue guide provides detailed protocols.

Prevention: The Best Treatment

Preventing temperature-related emergencies is far more effective than treating them. The CDC recommends staying hydrated — drink water before you feel thirsty during heat exposure — taking breaks in shade or air conditioning, wearing lightweight and light-colored clothing, and avoiding strenuous outdoor activity during the hottest part of the day (10 AM to 4 PM). Use the buddy system when working in extreme conditions; check on elderly neighbors and people without air conditioning during heat waves.

For cold weather, the CDC advises wearing multiple loose layers, a hat or hood (significant heat is lost from an uncovered head), and waterproof outer layers. Avoid cotton clothing for outdoor activity in cold weather — cotton retains moisture and accelerates heat loss. Wool, fleece, and synthetic materials are superior. Stay dry, seek shelter from wind, and avoid alcohol and tobacco, which impair thermoregulation.

FAQ

What is the difference between heat exhaustion and heat stroke?
The key distinguishing feature is mental status. Heat exhaustion presents with heavy sweating, weakness, and nausea but normal mentation. Heat stroke requires brain dysfunction — confusion, seizures, or unconsciousness — plus a core temperature over 40°C (104°F).

How long does it take to develop hypothermia in cold water?
In water at 10°C (50°F), incapacitation occurs within 15 minutes and death within 30 to 60 minutes. In ice water, survival time may be as short as 15 to 30 minutes. Protective gear and body fat increase survival time.

Should I rub frostbitten skin to warm it?
No. Never rub or massage frostbitten tissue. Ice crystals in the cells cause mechanical damage when rubbed. Rewarm gently with body heat or warm water.

Can you get hypothermia in temperatures above freezing?
Yes. Hypothermia commonly occurs in temperatures between 0°C and 10°C (32°F to 50°F), especially when wind chill, rain, or wet clothing accelerate heat loss. The CDC warns that hypothermia can develop at cool temperatures, particularly in older adults, infants, and people who are ill or malnourished.

Do I need to see a doctor for heat exhaustion?
Mild heat exhaustion usually resolves with rest, cooling, and fluids. If symptoms do not improve within 30 minutes, if vomiting prevents fluid intake, or if confusion develops, seek medical evaluation. Untreated heat exhaustion can progress to heat stroke.

Internal links: For water-related temperature emergencies, see our drowning rescue guide. For pediatric-specific temperature considerations, see first aid for children.