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Heat and cold emergencies

Four conditions that share a common structure: a warning stage and a life-threatening stage. Getting the two confused in either direction — heat or cold — determines whether the person in front of you gets first aid or emergency care. This page covers the key signs that separate serious from dangerous.

Skill AreaFirst Aid and Health
TopicHeat and Cold Emergencies
TypeInfo Page

01 — Heat emergencies

Heat exhaustion and heat stroke are not the same emergency. One you manage; the other requires 911.

Heat exhaustion

  • SkinCool, moist, pale or flushed — still sweating
  • Mental statusAlert, may feel dizzy, weak, anxious
  • TemperatureBelow 104°F
  • Other signsHeadache, nausea, muscle cramps
  • ActionMove to cool place; hydrate; cool compresses; monitor closely
  • Call 911If vomiting, altered responsiveness, or no improvement

Heat stroke

  • SkinHot, dry — sweating has stopped
  • Mental statusConfused, agitated, slurred speech, may lose consciousness
  • Temperature104°F or higher
  • Other signsRapid pulse, rapid breathing, nausea, flushing
  • ActionCall 911 immediately; aggressive cooling by any means available
  • Do notGive fluids if altered mental status — choking risk

The key clinical distinction between heat exhaustion and heat stroke is skin status and mental state. A person with heat exhaustion is still sweating — the cooling mechanism is working, just overwhelmed. A person with heat stroke has stopped sweating because the cooling system has failed entirely. Body temperature rises rapidly and can reach 106°F within 10 to 15 minutes. At this point, permanent disability and death are real risks without immediate intervention.

Heat stroke is a medical emergency. Call 911 immediately. While waiting for emergency services, cool the person by every means available: move them to shade or air conditioning, remove excess clothing, apply cold wet cloths or ice packs to the neck, armpits, and groin, and fan them to promote evaporative cooling. If they are conscious and not confused, offer cool fluids. If their mental status is altered, do not give fluids due to the risk of aspiration.

Heat illness spectrum

Heat cramps are painful muscle spasms from fluid and salt loss, usually in legs or abdomen. They are a warning sign. Move to a cool place, rest, and slowly replace fluids and electrolytes. Heat cramps can progress to heat exhaustion, which can progress to heat stroke without intervention at each stage.

02 — Hypothermia

When shivering stops in a cold environment, that is not improvement. It is a warning sign of severe hypothermia.

Critical counterintuitive sign

Shivering is the body's active mechanism for generating heat. In severe hypothermia, the body can no longer sustain the metabolic effort of shivering and it stops. A person who was shivering and then stops shivering in a cold environment has not improved — they have likely progressed to severe hypothermia. Call 911 immediately.

Hypothermia occurs when core body temperature falls below 95°F (35°C). It does not require extreme cold — it can develop in wet or windy conditions, from cold water immersion, or even from prolonged exposure to temperatures that feel merely cold. Early signs include shivering, slurred speech, confusion, stumbling, and low energy. As it progresses, shivering stops, coordination worsens severely, pulse slows, breathing becomes shallow, and the person may lose consciousness.

The Red Cross and AHA 2024 guidelines are clear on rewarming priorities:

  • Move the person to a warm environment. If that is not possible, insulate them from the cold ground, shield from wind, and cover the head and neck.
  • Remove wet clothing gently. Wet fabric accelerates heat loss. Replace with dry clothing, blankets, or any dry insulating material.
  • Warm the core (trunk, abdomen, and neck) first — not the hands and feet. Warming the extremities first drives cold blood from the limbs to the core, which can dangerously lower core temperature further and cause heart arrhythmias.
  • Rewarm slowly. Do not immerse in warm water. Rapid rewarming causes dangerous heart rhythms. Wrap heat sources (hot water bottles, chemical heat packs) in cloth before applying.
  • If the person is alert, offer warm (not hot) drinks and high-calorie food. Do not give alcohol — it increases heat loss despite the feeling of warmth. Do not give caffeine.
  • Call 911 for any person who has lost consciousness, has stopped shivering, or is showing signs of severe hypothermia. Even if they appear stable, monitor breathing continuously — hypothermia can make pulse and breathing very difficult to detect.

03 — Frostbite

Lukewarm water, not heat. And do not rewarm if there is any risk the tissue will refreeze.

Frostbite is the freezing of skin and underlying tissue, most commonly affecting fingers, toes, ears, and the nose. Signs include pale, waxy, or grayish skin that feels cold and hard to the touch, with numbness or loss of sensation in the affected area. As it progresses, the skin may appear blue or mottled and blisters may form.

The AHA and Red Cross 2024 guidelines recommend rewarming frostbitten tissue in clean lukewarm water at 37 to 40 degrees Celsius (99 to 104 degrees Fahrenheit) as soon as possible, provided there is no risk of the tissue refreezing. If the person must continue in the cold and there is a chance the tissue could refreeze, do not rewarm it. Tissue that freezes, thaws, and refreezes sustains far more damage than tissue that remains frozen until definitive care is available.

  • Get the person into a warm environment and out of cold and wind.
  • Remove constricting items from the affected area: rings, watches, tight footwear.
  • Do not rub the frostbitten area. Rubbing damages the frozen tissue.
  • Do not walk on frostbitten feet unless absolutely necessary for safety. Weight-bearing damages frozen tissue.
  • If rewarming is appropriate (no refreezing risk), immerse gently in lukewarm water at 37–40°C (99–104°F). This temperature range feels comfortably warm but not hot. Hot water will burn tissue that cannot feel pain.
  • Do not break blisters that form. Cover the area with dry, sterile gauze. Place gauze between frostbitten fingers or toes to keep them separated.
  • Seek emergency medical care as soon as possible. Frostbite requires professional evaluation to assess the depth of tissue injury.

If a person has both hypothermia and frostbite, treat the hypothermia first. Rewarming frostbitten extremities in a person with hypothermia drives cold blood to the core and worsens the systemic condition.

Quick reference

  • Heat exhaustion: still sweating, cool/moist/pale skin, alert — move to cool place, hydrate, monitor
  • Heat stroke: sweating stopped, hot/dry skin, confused or altered mental status — call 911, cool aggressively by any means
  • Do not give fluids to a person with altered mental status from heat stroke — aspiration risk
  • Hypothermia: shivering stops = severe progression, not improvement — call 911
  • Rewarm the core first, not the extremities; warming extremities first can cause dangerous heart arrhythmias
  • No alcohol for hypothermia — it increases heat loss despite the feeling of warmth
  • Frostbite: lukewarm water (37–40°C), not hot water; do not rewarm if refreezing risk; do not rub; do not walk on frozen feet
  • Hypothermia takes priority over frostbite if both are present

Primary sources

  1. Red Cross — 2024 First Aid Guidelines Summary: Frostbite: rewarm in lukewarm water 37–40°C as soon as possible if no refreezing risk; protect from further injury; avoid walking on frozen feet. Hypothermia: remove saturated clothing, warm core, insulate from ground, no rapid rewarming; high-calorie food and warm drinks for alert patients with mild hypothermia.
  2. CDC / NIOSH — Heat-Related Illnesses: Heat stroke is the most serious; body temperature can rise to 106°F or higher within 10–15 minutes; heat stroke can cause permanent disability or death without emergency treatment; heat exhaustion involves excessive sweating and fluid loss.
  3. Red Cross — Hypothermia: Move to warm place; remove wet clothes; rewarm slowly; warm core first not extremities; no alcohol (increases heat loss); no caffeine; rapid warming causes dangerous heart arrhythmias.
  4. Mayo Clinic — Heatstroke: First Aid: 104°F or greater; confusion and altered mental status; hot dry skin or heavy sweating; call 911 immediately; cool by any means available including immersion, cool damp sheets, cold packs.
  5. Mayo Clinic — Hypothermia: First Aid: Shivering may stop as body temperature drops — critical sign of progression to severe; apply warm compresses to neck, chest, and groin; focus on center of the body for warming.