Hypothermia: Symptoms, Causes, and Risk Factors

Hypothermia is not simply “feeling really cold.” It is a medical emergency in which the body loses heat faster than it can replace it, causing the core temperature to fall below 95°F (35°C). At that point, the brain, heart, lungs, and other organs can no longer work normally. Without prompt treatment, hypothermia may cause respiratory failure, cardiac arrest, organ damage, and death.

Although hypothermia is closely associated with snowstorms and frozen mountain trails, it can develop in less dramatic conditions. A rain-soaked hiker, an older adult living in a poorly heated home, a boater who falls into cold water, or an exhausted worker wearing damp clothing may all be at risk. Hypothermia can even occur when the outdoor temperature is above 40°F if rain, sweat, wind, or cold-water immersion causes the body to lose enough heat.

Understanding the symptoms, causes, and risk factors of hypothermia can help you recognize trouble earlybefore confusion sets in and the person starts insisting that everything is perfectly fine while attempting to button a jacket with the coordination of a sleepy lobster.

What Is Hypothermia?

The human body normally keeps its internal temperature within a narrow range. A control center in the brain called the hypothalamus receives temperature signals and activates defenses against cold. Blood vessels near the skin narrow to reduce heat loss, muscles begin to shiver, and metabolism increases to produce additional warmth.

These defenses work only for so long. When exposure continues, stored energy is depleted and heat loss overtakes heat production. The core temperature begins to drop, progressively interfering with movement, judgment, breathing, circulation, and consciousness.

How the Body Loses Heat

Heat can escape from the body through several pathways:

• Radiation: Heat naturally moves from the warm body into a colder surrounding environment.
• Conduction: Direct contact with cold water, frozen ground, metal, or another cold surface pulls heat away from the body.
• Convection: Moving air or water repeatedly replaces the warmer layer next to the skin, accelerating heat loss.
• Evaporation: Moisture from rain, sweat, or wet clothing cools the body as it evaporates.

Water conducts heat away from the body far more efficiently than air, which is why cold-water immersion is especially dangerous. Wind is another major problem because it strips away the thin layer of warm air surrounding the skin. The thermometer may provide the headline, but wind and moisture often write the alarming fine print.

Symptoms of Hypothermia

Hypothermia symptoms vary according to the person, the duration of exposure, underlying health conditions, and the degree of cooling. Symptoms may progress gradually, and the affected person may not recognize what is happening because low body temperature impairs judgment.

Early or Mild Hypothermia Symptoms

Mild hypothermia generally corresponds to a core temperature between approximately 90°F and 95°F, although treatment in the field should be guided by the person’s condition rather than waiting for a perfect thermometer reading.

Early warning signs may include:

• Persistent or uncontrollable shivering
• Cold, pale skin
• Fatigue or unusual sleepiness
• Numb fingers and difficulty using the hands
• Clumsiness, stumbling, or reduced coordination
• Slurred or slowed speech
• Irritability, apathy, or poor judgment
• Mild confusion or memory problems
• Rapid breathing followed by progressively slower breathing

Shivering is the body’s emergency furnace. It helps generate heat through repeated muscle activity, but it also consumes energy. Someone who has been shivering forcefully for a long time may eventually become exhausted.

Moderate Hypothermia Symptoms

As the core temperature falls further, the nervous system becomes increasingly impaired. Moderate hypothermia may cause:

• Worsening confusion or disorientation
• Marked loss of coordination
• Difficulty walking or standing
• Slurred, incoherent, or unusually quiet speech
• Slow breathing and a weak pulse
• Reduced responsiveness
• Decreasing or absent shivering
• Abnormal behavior or hallucinations

When a cold person stops shivering, it does not necessarily mean the person is warming up. In a confused, weak, or drowsy individual, the disappearance of shivering may indicate that the body is losing its ability to produce heat. That is an emergency, not a victory lap.

Severe Hypothermia Symptoms

Severe hypothermia can affect every major organ system. Warning signs include:

• Loss of consciousness
• Very slow, shallow, or apparently absent breathing
• A pulse that is extremely weak or difficult to detect
• Dilated pupils
• Rigid muscles
• Dangerous heart rhythm abnormalities
• Fluid accumulation in the lungs
• Cardiac arrest

A severely hypothermic person may appear lifeless because breathing and circulation can become exceptionally slow. Call 911 immediately, follow the dispatcher’s instructions, and begin CPR if the person is unresponsive and not breathing normally. Use an automated external defibrillator when available and appropriate.

Hypothermia Symptoms in Babies

Babies cannot communicate that they are becoming dangerously cold and may not shiver as noticeably as adults. Signs can include bright red or unusually pale cold skin, very low energy, weak crying, poor feeding, unusual quietness, limpness, and sleepiness. A cold, lethargic infant needs urgent medical evaluation.

Common Causes of Hypothermia

Prolonged Exposure to Cold Weather

Remaining outdoors without adequate clothing is the classic cause of hypothermia. Hikers, hunters, campers, athletes, emergency responders, construction crews, utility workers, delivery workers, and people experiencing homelessness may be exposed for extended periods.

Temperature alone does not determine risk. Wind, precipitation, altitude, shade, exhaustion, and the availability of shelter all matter. A calm, dry winter afternoon is very different from the same temperature accompanied by driving rain and a stiff wind.

Cold-Water Immersion

Falling from a boat, breaking through ice, attempting a cold-water swim, or remaining in floodwater can cause rapid heat loss. Initial cold shock may trigger gasping, panic, and rapid breathing. As exposure continues, muscle control deteriorates, making it harder to swim, hold onto a flotation device, or climb out of the water.

Anyone boating in cold conditions should wear a properly fitted life jacket rather than merely keeping one nearby as decorative equipment. Getting out of the water, protecting the airway, and obtaining emergency help are immediate priorities.

Wet Clothing and Sweat

Wet clothing loses much of its insulating value. Rain, melting snow, perspiration, or an accidental soaking can cool the body even when the weather does not feel brutally cold. Overdressing during strenuous activity can also create risk because sweat accumulates inside clothing and later cools the body when activity slows.

Cold Indoor Environments

Hypothermia can occur indoors, particularly during power outages or when people cannot afford adequate heating. Older adults, infants, people with limited mobility, and those with chronic medical conditions may become dangerously cold in homes that merely feel “chilly” to healthier occupants. Some older adults may develop hypothermia in indoor temperatures around 60°F to 65°F.

Illness, Injury, and Reduced Heat Production

Hypothermia is not always caused by dramatic environmental exposure. Medical conditions may reduce heat production, interfere with temperature regulation, or prevent someone from responding appropriately to cold. Possible contributors include low blood sugar, hypothyroidism, adrenal insufficiency, severe infection, malnutrition, stroke, neurological disease, and trauma.

Blood loss and shock can also impair circulation and heat production. A person who is injured and unable to move may lose heat through prolonged contact with cold ground, even when the surrounding air is relatively mild.

Hypothermia Risk Factors

Older Age

Older adults may have less insulating body fat, slower circulation, a reduced shivering response, and a lower metabolic rate. Chronic disease and medications may further interfere with temperature regulation. Mobility problems can make it difficult to add clothing, adjust a thermostat, or seek help.

Confusion caused by hypothermia may also be mistaken for dementia, fatigue, or ordinary aging. New confusion, clumsiness, or slurred speech in a cold environment should never be brushed aside.

Infancy and Early Childhood

Babies and young children lose heat relatively quickly because they have a larger surface area in relation to their body mass. They may also be unable to recognize danger, change wet clothing, or move to a warmer place without assistance.

Alcohol and Drug Use

Alcohol widens blood vessels near the skin, creating a temporary sensation of warmth while increasing heat loss. It also impairs judgment, balance, and the ability to recognize danger. Sedatives, opioids, and illicit drugs may reduce alertness or cause a person to remain motionless in a cold environment.

A warming shot of whiskey may sound cinematic, but it is poor first aid. Alcohol does not safely warm the core and should never be given to someone with suspected hypothermia.

Exhaustion, Dehydration, and Inadequate Nutrition

Shivering requires fuel. People who are exhausted, dehydrated, fasting, or undernourished have fewer resources available for heat production. Long hikes, outdoor labor, illness, and survival situations may combine several of these risks at once.

Low Body Weight and Limited Body Fat

People with very low body weight may have less natural insulation and fewer energy reserves. Eating disorders, chronic illness, and food insecurity can increase vulnerability.

Chronic Medical Conditions

Diabetes, poor circulation, heart disease, neurological disorders, endocrine conditions, dementia, and mobility limitations can increase the risk of hypothermia or make its symptoms harder to recognize.

Certain Medications

Some medicines may affect alertness, circulation, metabolism, or the body’s temperature response. These can include certain sedatives, antipsychotics, antidepressants, opioid pain medicines, and medications that affect blood pressure. People should not stop prescribed medication without medical advice, but those at elevated risk should discuss cold-weather precautions with a healthcare professional.

Outdoor Occupations and Unstable Housing

People who work outside, remain in unheated buildings, or lack reliable shelter face repeated exposure. Employers can reduce risk through worker training, scheduled warm-up breaks, dry replacement clothing, heated shelters, weather monitoring, and a buddy system for identifying symptoms before judgment becomes impaired.

What to Do for Suspected Hypothermia

Treat suspected hypothermia as an emergency, especially when the person is confused, drowsy, unable to walk normally, no longer shivering, or has slow breathing.

1. Call 911. Do not delay emergency care while attempting to rewarm someone with moderate or severe symptoms.
2. Move the person carefully. Get the person away from wind, rain, snow, cold water, or cold ground. Handle a severely cold person gently because the heart may be vulnerable to dangerous rhythms.
3. Remove wet clothing. Cut clothing away when necessary to avoid excessive movement, then replace it with dry layers.
4. Insulate the entire body. Use dry blankets, coats, sleeping bags, towels, or other available materials. Cover the head and neck while keeping the airway clear.
5. Warm the core gradually. Place warm, dry compresses around the chest, neck, armpits, or groin. Do not concentrate heat on the arms and legs.
6. Offer a warm drink only when safe. A person who is fully alert and able to swallow may be given a warm, sweet, nonalcoholic, noncaffeinated beverage.
7. Monitor breathing and responsiveness. Begin CPR and use an AED when indicated, following emergency-dispatch instructions and your level of training.

Do not rub or massage the person’s limbs, place them in a very hot bath, use a heating lamp, or apply direct high heat. Aggressive heating can damage cold skin and may send cold blood from the extremities back toward the core. Do not assume that a person can simply “walk it off.”

How Hypothermia Is Diagnosed and Treated

Healthcare professionals consider the circumstances of exposure, symptoms, physical findings, and core temperature. In the field, accurate core-temperature measurement may be difficult, so treatment should not be postponed when the clinical signs strongly suggest hypothermia.

Hospital treatment depends on severity. Mild cases may improve with dry insulation, warm surroundings, and passive rewarming. More serious cases may require forced-air warming blankets, warmed intravenous fluids, heated humidified oxygen, internal irrigation with warmed fluids, or extracorporeal blood rewarming. In critical cases, an ECMO or heart-lung bypass system may warm and oxygenate the blood while supporting circulation.

Possible Complications

Untreated hypothermia may lead to abnormal heart rhythms, cardiac arrest, respiratory failure, kidney or liver injury, impaired blood clotting, aspiration, coma, and death. Frostbite may occur at the same time, particularly on the fingers, toes, ears, nose, and cheeks.

Recovery depends on the lowest body temperature, duration of exposure, underlying health, associated injuries, speed of rescue, and availability of advanced rewarming. Even a person who appears profoundly unresponsive may sometimes survive with prolonged, specialized resuscitation, which is one reason rescuers should contact emergency professionals immediately rather than making assumptions.

How to Prevent Hypothermia

• Check the forecast, wind chill, precipitation, and changing conditions before outdoor activity.
• Wear several loose layers rather than one bulky layer.
• Choose a moisture-managing base layer, an insulating middle layer, and a wind- and water-resistant outer shell.
• Protect the head, neck, hands, and feet with appropriate cold-weather gear.
• Replace wet clothing promptly.
• Take regular warm-up breaks during outdoor work or recreation.
• Avoid becoming drenched in sweat; remove or open layers before overheating.
• Carry dry clothing, high-energy food, water, an emergency blanket, and communication equipment.
• Use a buddy system and watch for stumbling, fumbling, mumbling, and unusual behavior.
• Wear a life jacket when boating or fishing in cold conditions.
• Avoid alcohol before or during cold exposure.
• Check on older adults, infants, and people living with unreliable heating during cold weather.

Preparation may feel less exciting than improvising a wilderness rescue with a granola bar and one mysteriously damp sock. It is, however, much more effective.

Practical Experiences and Lessons From Cold-Exposure Scenarios

Experience 1: The Rainy Hike That Did Not Feel Cold Enough

Imagine two friends beginning an afternoon hike when the temperature is 46°F. Neither considers it true winter weather. A steady rain begins, the trail becomes windy, and one hiker’s cotton sweatshirt absorbs water. After several hours, he is shivering hard, dropping items, and giving strangely vague answers about the route.

The essential lesson is that hypothermia does not require a blizzard. Cool air, wet clothing, wind, and fatigue can form a dangerous combination. The fumbling hands and mental changes matter more than whether the air temperature looks impressive on a weather app. The correct response is to stop the hike, find shelter, replace wet layers, insulate the person, and request help if symptoms do not quickly improve or include confusion.

Experience 2: An Indoor Emergency During a Power Outage

Consider an older adult living alone after a winter storm cuts electricity for two days. The home gradually cools to the low 60s. A relative calls and notices slow speech, unusual irritability, and confusion. The older adult says everything is fine and does not feel especially cold.

This scenario demonstrates why indoor hypothermia is easy to overlook. Older people may not sense temperature changes as strongly, may produce less body heat, and may have health conditions or medications that increase vulnerability. A sudden behavioral change during cold weather deserves immediate attention. Family members and neighbors should check the actual indoor temperature, arrange a heated location, and seek medical help when confusion or coordination problems appear.

Experience 3: A Boater Falls Into Cold Water

A kayaker capsizes on a chilly spring morning. The air is mild, but the water remains dangerously cold. The first reaction is gasping and frantic breathing. After being helped into another boat, the kayaker says he can paddle back but cannot grip the paddle properly and begins slurring his words.

The lesson is that rescue does not end when someone leaves the water. Wet clothing, wind, and continued cooling can cause the core temperature to keep falling. The person should be protected from wind, handled gently, stripped of wet clothing when possible, insulated, and evaluated urgently. A life jacket is critical because swimming ability and hand function can deteriorate long before severe hypothermia is obvious.

Experience 4: The False Warmth of Alcohol

At an outdoor winter celebration, a guest who has been drinking removes his coat because he feels hot. His face looks flushed, but his speech becomes more confused and he repeatedly stumbles. Friends initially assume he is only intoxicated.

Alcohol can disguise and worsen hypothermia. It increases heat loss near the skin while reducing judgment and self-protective behavior. Because intoxication and hypothermia can both cause slurred speech, poor balance, and confusion, cold exposure should be treated seriously rather than blamed entirely on alcohol. Move the person indoors, call for emergency help when symptoms are significant, and do not provide additional alcohol.

The Shared Lesson

Across these experiences, the most important pattern is not a particular temperature. It is a change in function. Shivering, stumbling, fumbling, confusion, exhaustion, and slurred speech are signals that the body and brain are struggling. People in the early stages may minimize the problem, while those in later stages may be unable to make safe decisions at all.

Cold-weather safety therefore depends on watching one another. A buddy may notice clumsy hands or strange speech before the affected person understands that anything is wrong. Recognizing that change and acting early can turn a potential medical disaster into an inconvenient story about blankets, dry socks, and the best cup of warm cocoa anyone has ever tasted.

Conclusion

Hypothermia occurs when heat loss overwhelms the body’s ability to stay warm, lowering the core temperature below 95°F. Cold weather and cold-water immersion are common causes, but wet clothing, wind, exhaustion, illness, intoxication, immobility, and poorly heated indoor spaces can also create dangerous conditions.

Persistent shivering, fumbling hands, slurred speech, confusion, drowsiness, and poor coordination should never be ignored. When symptoms are serious, call 911, prevent further heat loss, remove wet clothing, insulate the person, warm the core gradually, and monitor breathing. Prompt recognition and careful rewarming can save a life.

Information basis: This article synthesizes guidance from the CDC, CDC/NIOSH, National Institutes of Health, National Institute on Aging, MedlinePlus, National Weather Service, OSHA, American Red Cross, Mayo Clinic, Cleveland Clinic, Johns Hopkins Medicine, Merck Manual, American Academy of Family Physicians, NCBI Bookshelf, and Wilderness Medical Society guidance.