Hypothermia
Based on Wikipedia: Hypothermia
In the final stages of freezing to death, something strange happens. People start taking off their clothes.
It's called paradoxical undressing, and it occurs in twenty to fifty percent of hypothermia deaths. The dying person, now deeply confused and disoriented, becomes convinced they're overheating. They strip off their jacket, their sweater, their shirt—the very things keeping them alive. Rescuers trained in mountain survival expect this. But in cities, when someone is found dead and undressed in winter, investigators sometimes wrongly assume sexual assault.
This bizarre behavior hints at something fundamental about hypothermia: it's not just about being cold. It's about the brain losing its grip on reality as the body's core temperature drops below 35 degrees Celsius (95 degrees Fahrenheit). The word itself comes from the Greek—hypo meaning "under" and therme meaning "heat." Its opposite is hyperthermia, which is overheating. But while overheating kills you relatively straightforwardly, freezing to death takes you through a strange psychological journey first.
The Three Stages of Freezing
Your body normally maintains its temperature within a narrow band: 36.5 to 37.5 degrees Celsius (97.7 to 99.5 degrees Fahrenheit). This isn't just a comfortable range—it's the temperature at which your enzymes work properly, your heart beats correctly, and your brain thinks clearly. Drop below that range, and things start going wrong in stages.
In mild hypothermia, when your core temperature falls to between 32 and 35 degrees Celsius (90 to 95 degrees Fahrenheit), your body fights back hard. You shiver violently—an involuntary muscle contraction that can generate surprising amounts of heat. Your blood pressure rises. Your heart races. Blood vessels near your skin constrict, pulling warm blood toward your vital organs. You might feel confused, have trouble speaking clearly, or lose fine motor control in your fingers. Your liver starts dumping glucose into your bloodstream, trying to fuel the shivering.
This is your body's emergency response, and it works—for a while.
In moderate hypothermia, between 28 and 32 degrees Celsius (82 to 90 degrees Fahrenheit), the shivering stops. This isn't because you're warming up. It's because your muscles are too cold and exhausted to keep contracting. Your heart rate drops into the thirties. Your breathing slows. You become increasingly confused, combative, and irrational. This is when paradoxical undressing typically begins. You might also experience something called "terminal burrowing" or "hide-and-die syndrome"—an instinct to crawl into small, enclosed spaces like a hibernating animal. Researchers believe this is a primitive brain stem response, triggered when higher brain functions shut down.
In severe hypothermia, below 28 degrees Celsius (82 degrees Fahrenheit), you may hallucinate. Your pupils dilate and stop responding to light. Your pulse becomes nearly undetectable. Your skin turns cold and inflamed. Your heart may start beating erratically—a condition called ventricular fibrillation—or it may simply stop. You look dead. You may, in fact, be dying.
But here's the remarkable thing: you might not be dead yet.
The Cold Paradox
There's an old saying in emergency medicine: "You're not dead until you're warm and dead."
The same cold that kills you can also preserve you. As your body temperature drops, your metabolism slows dramatically. Your brain needs less oxygen. Your heart needs less fuel. In a sense, you're being refrigerated from the inside out—and this can buy time.
The lowest documented core temperature from which someone has survived is 12.7 degrees Celsius (54.9 degrees Fahrenheit). The survivor was a two-year-old Polish boy named Adam. At that temperature, his brain was barely functioning, his heart may have stopped entirely, and by every conventional measure he should have been dead. But the cold that brought him to the edge of death also held him there, suspended, until doctors could warm him back to life.
People have survived more than six hours of cardiopulmonary resuscitation (CPR)—chest compressions and rescue breathing—when hypothermia is involved. In normal circumstances, if your heart stops for more than a few minutes without CPR, and more than fifteen or twenty minutes even with it, brain death is virtually certain. The cold changes the math.
This is why modern treatment protocols call for continuing resuscitation efforts until the patient's core temperature reaches at least 32 degrees Celsius (90 degrees Fahrenheit). Only then, if there's still no heartbeat and no other signs of recovery, do doctors consider stopping. There's one exception: if blood potassium levels exceed 12 millimoles per liter at any point, survival is essentially impossible, and resuscitation can be discontinued.
How Heat Leaves the Body
To understand hypothermia, you need to understand heat.
Your body generates warmth primarily in two places: your muscles (including your heart) and your liver. When you're active, your muscles can produce over 1,200 watts of heat—enough to power a small space heater. Even at rest, your metabolism keeps your core warm.
But heat is constantly escaping. About ninety percent leaves through your skin; the remaining ten percent exits through your lungs when you exhale warm, moist air. The rate of loss depends on physics: convection (air or water moving past your skin), conduction (direct contact with cold surfaces), and radiation (heat energy simply radiating away into cooler surroundings).
Water is particularly dangerous. It conducts heat away from your body roughly twenty-five times faster than air at the same temperature. A water temperature of 10 degrees Celsius (50 degrees Fahrenheit) feels bracing on a summer day—you might swim in it comfortably for a while. But if you can't get out, you'll be dead within an hour. Near-freezing water can kill in fifteen minutes.
This is what happened to passengers on the Titanic. The water that night was minus 2 degrees Celsius (28 degrees Fahrenheit)—below the normal freezing point of fresh water because the salt in seawater lowers its freezing temperature. Most people who went into that water died within fifteen to thirty minutes.
But here's something crucial: they didn't die from hypothermia in the clinical sense. They died from the body's reactions to cold water.
Cold Water Kills Fast—But Not How You'd Think
When you plunge into freezing water, several things happen almost immediately.
First comes the cold shock response. You gasp involuntarily. You hyperventilate—breathing rapidly and uncontrollably. Your blood pressure spikes. Your heart races and may develop dangerous arrhythmias. About twenty percent of cold water drowning victims die within two minutes from this response alone. They gasp, inhale water, and drown before hypothermia even begins.
If you survive the initial shock, cold incapacitation sets in within fifteen to thirty minutes. Your body, trying to protect your vital organs, shuts down blood flow to your arms and legs. Your muscles stop working properly. You lose the ability to swim or grip a floating object. Another fifty percent of victims die during this phase—not from the cold penetrating their core, but from simple drowning when they can no longer keep their head above water.
True hypothermia—the dangerous drop in core temperature—takes longer to develop. If you're wearing a life jacket that keeps your head above water, you might survive the shock and incapacitation phases. Then, and only then, does the slow cooling of your core become the primary threat.
This is why survival training for cold water focuses on the first few minutes: stay calm, control your breathing, get your face out of the water, and don't try to swim unless safety is very close. Fighting the water wastes the muscle coordination you'll need later.
Who Freezes?
Hypothermia kills at least 1,500 Americans each year. The victims are disproportionately male and elderly. But anyone can die from the cold under the wrong circumstances.
Alcohol is a major factor, complicating between 33 and 73 percent of hypothermia cases. This seems paradoxical because drinking makes you feel warm. But that warmth is an illusion—and a deadly one.
When you drink alcohol, your blood vessels dilate. Blood flows to your skin, making you flush and feel heated. But that blood is now radiating its warmth directly into the cold environment. Meanwhile, alcohol impairs your hypothalamus—the brain region that regulates body temperature—making you less likely to shiver and less able to recognize that you're in danger. Drunk people stumble outside in winter without coats, sit down in snowbanks because they feel fine, and never get up.
Homelessness is another major risk factor, for obvious reasons. But measuring hypothermia deaths among homeless populations is difficult because many deaths go unreported or are attributed to other causes.
Medical conditions matter too. Low blood sugar (hypoglycemia) can both cause and result from hypothermia, creating a dangerous feedback loop. An underactive thyroid gland (hypothyroidism) reduces your metabolic heat production. Severe infections (sepsis) can paradoxically cause either fever or hypothermia, and hypothermic sepsis patients tend to fare worse. Anorexia nervosa depletes the body fat that provides insulation and the muscle mass that generates heat.
Major trauma—car accidents, falls, violent injuries—often causes hypothermia even in moderately cold environments. Shock reduces blood flow, injury prevents movement, and blood loss accelerates cooling.
And there are the adventurers: hikers caught in sudden storms, divers who stay down too long, climbers who miscalculate. As outdoor recreation becomes more popular, these accidental exposures are likely to increase.
Treating the Frozen
If someone has mild hypothermia—they're shivering, alert, and able to move—treatment is straightforward. Get them out of the cold. Remove wet clothing. Give them warm drinks (not alcohol, which will only accelerate heat loss). Encourage them to move around; muscle activity generates heat. Wrap them in blankets. Their own shivering will do most of the work.
Moderate hypothermia is more serious. The person may have stopped shivering. They may be confused or drowsy. At this stage, warming from the outside alone may not be enough. Hospitals use warmed intravenous fluids, which deliver heat directly to the bloodstream. Heated blankets help, but the body's core needs warming that passive techniques can't provide.
Severe hypothermia requires aggressive intervention. The most effective treatment is extracorporeal membrane oxygenation, or ECMO—a machine that draws blood out of the body, warms it, oxygenates it, and pumps it back in. Cardiopulmonary bypass, similar to the heart-lung machines used in open-heart surgery, works on the same principle. These technologies can raise core temperature by several degrees per hour.
Survival rates with ECMO or bypass hover around fifty percent—not great, but remarkable considering that these patients would otherwise be dead.
One crucial principle: move hypothermic patients gently. Their hearts are cold and irritable, prone to suddenly developing fatal arrhythmias if jostled. Rescuers are trained to avoid rough handling, even during CPR.
The Heart on Ice
Cold does strange things to the heart.
As core temperature drops, the heart slows down—sometimes to rates in the thirties or below, when a normal resting heart rate is sixty to one hundred beats per minute. But the heart doesn't just slow; it becomes electrically unstable.
On an electrocardiogram (ECG), the electrical tracing of heartbeats, hypothermia produces a distinctive pattern called the Osborn J wave—a characteristic bump in the signal that experienced clinicians recognize immediately. But this pattern can look dangerously similar to an ST-elevation myocardial infarction, which is the electrical signature of a heart attack.
This matters because heart attacks are often treated with thrombolytic drugs—clot-busting medications that can save lives when a blocked artery is starving the heart of oxygen. But hypothermia causes its own clotting problems, and giving thrombolytics to a hypothermic patient makes the bleeding worse. The Osborn J wave is a warning: this patient is cold, not having a heart attack. Warm them up first.
Below 28 degrees Celsius (82 degrees Fahrenheit), the heart frequently develops ventricular fibrillation—a chaotic electrical storm that makes the heart quiver uselessly instead of pumping. Below 20 degrees Celsius (68 degrees Fahrenheit), it may stop entirely: asystole, the flatline of movies and television.
When rescuers find someone this cold, checking for a pulse requires patience. The heart may be beating only a few times per minute, too faint and slow to detect quickly. The American Heart Association recommends feeling for a pulse for at least thirty to forty-five seconds before concluding it's absent and beginning CPR. Some experts say sixty seconds.
War and Cold
Hypothermia has shaped history. Military campaigns have been won and lost in the snow.
Napoleon's 1812 invasion of Russia began with over 600,000 soldiers. By the time the remnants of his army retreated from Moscow, fewer than 100,000 remained. Combat accounted for some losses, but the brutal Russian winter killed far more. Soldiers froze in their tracks. Horses collapsed. The Grande Armée simply dissolved into the ice.
The German invasion of the Soviet Union in 1941 met a similar fate. Operation Barbarossa was supposed to be a quick victory, concluded before winter. But the Russian mud season slowed the advance, and then the cold arrived. German troops, equipped for a summer campaign, froze in temperatures that dropped below minus 30 degrees Celsius (minus 22 degrees Fahrenheit). Weapons jammed. Vehicles wouldn't start. Frostbite and hypothermia claimed tens of thousands.
Even in smaller conflicts, cold has been decisive. The Korean War saw numerous cold weather casualties. The Falklands War, fought in the South Atlantic winter, tested British troops' endurance in wet, freezing conditions. Modern militaries now train extensively for cold weather operations and equip soldiers accordingly—lessons learned at terrible cost.
Other Ways the Cold Hurts
Hypothermia isn't the only cold injury. Several related conditions can occur alone or alongside dropping core temperature.
Frostbite is the freezing of tissue. When ice crystals form inside cells, they rupture cell membranes and kill the tissue. Frostbite typically affects extremities—fingers, toes, ears, nose—because the body sacrifices these parts first to protect the core. Severe frostbite requires amputation.
Frostnip is a milder version: surface cooling without actual freezing. The skin turns pale and numb but recovers fully once warmed.
Chilblains result from repeated exposure to cold temperatures just above freezing. They cause permanent damage to small blood vessels in the skin, leading to redness, itching, and inflammation that recurs with each subsequent cold exposure. Chilblains typically appear on cheeks, ears, fingers, and toes.
Trench foot, also called immersion foot, comes from prolonged exposure to cold water that isn't quite freezing. It was epidemic in the trenches of World War One, where soldiers stood for days in cold, waterlogged mud. The tissue doesn't freeze, but prolonged cold and moisture damage blood vessels and nerves. Severe cases require amputation.
Staying Warm
Prevention is straightforward but frequently ignored.
Stay dry. Wet clothing loses most of its insulating value. Wool and synthetic fabrics retain some warmth when wet; cotton becomes nearly useless. This is why experienced outdoor enthusiasts say "cotton kills." Moisture-wicking base layers—made from materials like polypropylene or polyester—pull sweat away from the skin before it can sap heat.
Dress in layers. Multiple thin layers trap air between them, providing better insulation than a single thick garment. Layers also let you adjust: strip off a jacket when you're working hard and sweating, add it back when you stop.
Wear loose clothing. Tight garments restrict blood flow, reducing the warm blood that reaches your skin and extremities.
Cover your head—but don't overestimate its importance. The old claim that you lose most of your body heat through your head is a myth. You lose heat through any uncovered skin in proportion to its surface area. Your head is about ten percent of your body's surface, so it accounts for roughly ten percent of heat loss. The myth likely originated from military studies where subjects wore insulated suits but no hats, making the head appear to be a disproportionate source of heat loss.
That said, covering your head still matters, especially for infants, whose heads are proportionally larger relative to their bodies.
If you drink alcohol outdoors in cold weather, ensure someone sober is watching out for the group. Alcohol impairs judgment about both the cold and your own condition. Many hypothermia deaths involve someone who felt fine, stepped outside "just for a minute," and never made it back inside.
Prepare for conditions worse than expected. Weather changes. Plans go wrong. The storm that wasn't forecast arrives anyway. Carrying extra warm layers, emergency shelter materials, and high-energy food costs little and weighs less. Dying alone in the cold costs everything.
The Strangeness of Freezing
Perhaps what makes hypothermia so unsettling is how it distorts the mind.
The euphoria reported by some freezing victims seems almost merciful—a final kindness from a dying brain. But other symptoms are deeply disturbing: the aggression, the paradoxical conviction that you're overheating as you freeze, the animal instinct to burrow into a small space and hide.
In George Saunders' short story "Tenth of December," a dying man trudging through snow reflects on the cold claiming his body, his thoughts fragmenting as his brain cools. Fiction often captures what medical literature cannot: the subjective experience of becoming someone else, someone simpler and more primitive, as the cold does its work.
Understanding hypothermia means understanding that temperature isn't just about comfort. It's about who we are. Our personalities, our judgment, our very consciousness depend on warmth. Take that away, degree by degree, and something fundamental changes before the heart finally stops.
The cold doesn't just kill your body. It first kills your self—the person you were before you started to freeze.