Heat and cold emergencies: recognition and response

Key points#

• Heat and cold illness are spectrums: the urgent question is whether someone has crossed from the early stage (heat exhaustion, mild cold stress) into the dangerous one (heat stroke, hypothermia).
• The most important red flag in both directions is a change in mental state. Confusion, slurred speech, or loss of consciousness in a hot or cold person means call emergency services now.
• Heat exhaustion: move to cool, rest, hydrate, cool the skin; escalate if there is no improvement in about an hour or any confusion. Heat stroke: call emergency services and cool aggressively while you wait.
• Hypothermia: a body temperature below 95°F (35°C) is a medical emergency; move to warmth, remove wet clothing, warm the core gently, and call for help. Frostbite: protect the area, do not rub it or use direct heat, avoid refreezing, and get medical care.

Most of us picture temperature emergencies as rare, dramatic events. In practice they usually creep up slowly and without fanfare, and that is what makes them dangerous. A teenager at an August soccer tournament or an older neighbor in an apartment without air conditioning can slide from uncomfortable to genuinely in danger without a clear alarm going off. The useful skill is not memorizing every symptom; it is recognizing the line where the body's own thermostat is failing, because that is where first aid stops being enough and emergency care begins. This guide walks through that line in both directions, hot and cold.

The two heat illnesses, and the line between them#

Heat illness is a progression. The body keeps cool mainly by sweating and by moving blood to the skin, and in heat, especially with humidity or hard exertion, that system can be overwhelmed.

Heat exhaustion is the warning stage. The CDC describes the picture as heavy sweating, weakness, dizziness, headache, nausea, and muscle cramps, often with cool, moist, or clammy skin. A person with heat exhaustion still knows where they are and what is happening; they feel awful, but they are mentally intact. This stage is treatable on the spot, and treating it prevents the next one.

Heat stroke is the emergency, when the body can no longer shed heat and the core temperature climbs to a dangerous level. Two features separate it from heat exhaustion. The first is temperature: a very high body temperature, with skin that is often hot, and may be dry or still sweaty. The second, and the one that matters most, is the brain. Heat stroke causes a change in mental state such as confusion, agitation, slurred speech, a throbbing headache, fainting, seizures, or loss of consciousness. The American Red Cross frames altered mental status and a very high temperature as the signs that mean call emergency services.

If you remember one thing, remember this: confusion is the line. A hot, sweating person who is thinking clearly is probably in the heat-exhaustion stage. The moment they become confused, stop making sense, stop sweating despite the heat, or pass out, treat it as heat stroke and call for emergency help.

Responding to heat illness#

For heat exhaustion, the response is cooling and rest. Move the person somewhere cooler, ideally air-conditioned or at least shaded, have them stop activity and lie or sit down, and loosen or remove heavy clothing. Cool the skin with cool water, wet cloths, or a fan, and have them sip water if they are alert and not nauseated. The Red Cross advises watching closely, because if symptoms get worse or do not improve within about an hour, it is time to seek medical help. Vomiting, an inability to keep fluids down, or any change in alertness are reasons to escalate.

For heat stroke, the order changes. Call emergency services first, because this is life-threatening, then cool the person as aggressively as you safely can while help is on the way. Move them out of the heat and cool the whole body with whatever is available: cool water over the skin, wet sheets, ice packs to the neck, armpits, and groin, or immersion in cool water if that can be done safely. Do not give fluids by mouth to someone who is confused or not fully conscious, because of the choking risk. With heat stroke, the speed of cooling matters.

It also helps to know who is most at risk. The CDC lists older adults, infants and young children, pregnant people, people with chronic conditions, outdoor workers, athletes, and people without air conditioning as being at higher risk of heat-related illness. In those groups, take symptoms seriously earlier and check on them during heat waves.

Hypothermia: when the core gets too cold#

Cold emergencies run the same way, in the other direction. Hypothermia is what happens when the body loses heat faster than it can produce it.

Two points from MedlinePlus are worth holding onto. First, hypothermia is not only a wilderness or blizzard problem; anyone who spends time in the cold can develop it, and it can happen in cool indoor temperatures too, particularly in infants and older adults, with wet clothing, wind, and cold water all speeding heat loss. Second, there is a clear threshold: a body temperature below 95°F (35°C) is a medical emergency and can be deadly if it is not treated promptly.

The signs progress as the body cools. Early on, expect intense shivering, cold and pale skin, and clumsy or fumbling hands. As hypothermia deepens, the shivering can slow or stop, and the person becomes confused, drowsy, slurred in speech, or strangely apathetic. A cold person who has stopped shivering and is no longer thinking clearly is a serious sign, not an improvement. In an infant, watch for bright red but cold skin and very low energy.

If you suspect hypothermia, call emergency services for anyone who is confused, very drowsy, or has a suspected core temperature in the emergency range. While waiting, move the person somewhere warm, remove any wet clothing, and warm the center of the body first, the chest, neck, head, and groin, using dry blankets, layers, or skin-to-skin contact under a blanket. If they are alert and can swallow, a warm (not hot) sweet drink can help, but never alcohol. Handle them gently, and do not assume someone is beyond help just because they seem unresponsive and cold; the steps are still warming and emergency care.

Frostbite: cold injury to the skin and deeper tissue#

Frostbite is a different cold problem: actual freezing of the skin and the tissue beneath it, usually in the most exposed parts, fingers, toes, ears, nose, cheeks, and chin. It often travels with hypothermia in serious cold, so when you find one, look for the other.

MedlinePlus describes frostbitten skin as becoming white or grayish-yellow, feeling firm or waxy to the touch, and going numb. That numbness is part of the danger, because the person may not realize how much harm is happening. Frostbite can cause permanent damage, and in severe cases the loss of the affected part.

Here the do-nots matter as much as the dos, because they prevent more injury:

• Get the person somewhere warm and out of wet clothing.
• Do not rub or massage the frozen area, and do not rub it with snow; that tears the frozen tissue and makes the damage worse.
• Do not use direct or high heat such as a stove, fireplace, radiator, or heating pad. Numb skin cannot feel a burn, so it is easy to cause one. If rewarming is appropriate and you are safely away from the cold, do it gently with warm (not hot) water or body heat.
• Do not rewarm if the part might refreeze before you reach safety. A thaw-and-refreeze cycle is more damaging than staying frozen, so keep it protected and get to care.
• Do not walk on frostbitten feet or toes unless you must.

Then seek medical care, because frostbite benefits from proper assessment even when it seems to be recovering.

Staying safe in the extremes#

You do not have to be a clinician to make the call that matters most. In heat and cold alike, the early stage is the body's thermostat straining, which you can manage with cooling or warming and common sense, while the dangerous stage is when that defense fails and a change in how someone is thinking or behaving turns a temperature problem into an emergency call. For heat, tell apart the sweating, clear-headed person who needs shade, rest, and water from the confused or collapsed person who needs emergency services and cooling now. For cold, remember that a temperature below 95°F is an emergency, that a cold person who stops shivering and stops making sense is getting worse, and that frostbite is handled gently, never with rubbing or direct heat, and never with a refreeze.

For your own health, talk with your clinician. If you think someone is having a heat or cold emergency, call your local emergency number.