Hypothermia First Aid: Recognition and Rewarming
Hypothermia occurs when the body loses heat faster than it can produce it, causing core temperature to drop below 95 °F (35 °C). According to the CDC, hypothermia kills more than 1,300 Americans each year, with the highest rates among older adults, people experiencing homelessness, outdoor workers, and winter sports enthusiasts. The condition develops insidiously — a person who seems merely “cold” can slip into moderate or severe hypothermia within minutes without proper intervention.
This guide provides evidence-based first aid protocols for recognizing, treating, and preventing hypothermia, drawing on clinical guidelines from the CDC, the American Red Cross, and the Mayo Clinic.
Understanding the Three Stages of Hypothermia
The severity of hypothermia guides treatment decisions. Mild hypothermia occurs between 90–95 °F (32–35 °C). The hallmark is uncontrollable shivering as the body generates heat through muscle activity. The victim remains conscious but may appear clumsy, have cold and pale skin, and show impaired fine motor skills. Hand temperature drops noticeably, and the person may complain of numbness in the fingers and toes.
Moderate hypothermia ranges from 82–90 °F (28–32 °C). Shivering stops as the body depletes its energy reserves — a dangerous sign, not an improvement. The victim becomes confused, drowsy, or disoriented. Speech may be slurred, and coordination deteriorates significantly. The person may make irrational decisions such as removing clothing, a phenomenon known as paradoxical undressing caused by vasoconstriction failure.
Severe hypothermia is defined as a core temperature below 82 °F (28 °C). The victim is likely unconscious with no visible shivering. Pupils may be fixed and dilated. Pulse and respiration slow dramatically and may be difficult to detect. The American Heart Association warns that a severely hypothermic patient can appear clinically dead even when resuscitation is possible, giving rise to the principle “nobody is dead until warm and dead.”
Risk Factors and Vulnerable Populations
Anyone exposed to cold conditions can develop hypothermia, but certain groups are disproportionately affected. The CDC identifies infants and older adults as particularly vulnerable because of immature or diminished thermoregulation. People with medical conditions such as hypothyroidism, diabetes, Parkinson’s disease, spinal cord injuries, or cognitive impairments have reduced ability to sense or respond to cold. Alcohol consumption accelerates heat loss through vasodilation and impairs judgment, and this is a contributing factor in a significant percentage of urban hypothermia deaths. Medications including sedatives, antidepressants, and antipsychotics can further blunt the body’s ability to regulate temperature. Environmental factors such as wind chill, wet clothing, and cold water immersion dramatically increase risk. Water conducts heat away from the body 25 times faster than air of the same temperature.
Immediate First Aid for Hypothermia
The American Red Cross outlines a systematic approach to hypothermia first aid that prioritizes preventing further heat loss and gradually rewarming the victim. Take the following steps in order.
Step 1: Move the person out of the cold environment into a warm, dry location. If moving indoors is impossible, shelter them from wind and precipitation using a tarp, emergency blanket, or natural barriers such as a rock overhang or dense tree cover. Place insulating material between the victim and the ground — a sleeping pad, backpack, pile of dry leaves, or even a foam sit pad makes a significant difference because conductive heat loss through contact with cold ground is substantial.
Step 2: Remove wet clothing carefully — cut it off if necessary — and replace it with dry layers. Cover the head and neck, which are significant sources of heat loss since they have a rich blood supply and high surface-area-to-volume ratio. Use blankets, sleeping bags, emergency mylar blankets, or even layers of newspaper for insulation. The “burrito wrap” technique — placing the victim on an open sleeping bag, wrapping it around them, and covering with a waterproof outer layer — is an effective field method taught by NOLS Wilderness Medicine.
Step 3: For mild hypothermia, apply gentle external rewarming: warm compresses or hot water bottles wrapped in cloth to the armpits, groin, chest, and back. These areas have major blood vessels near the skin surface, allowing heat to transfer efficiently to the core. The American Red Cross warns against placing heat directly on the arms and legs because warming the extremities first can force cold blood back to the heart and core, potentially causing cardiac arrest — a phenomenon called “after drop.” Body-to-body contact with a volunteer who removes their clothing and shares a sleeping bag with the victim is an effective rewarming technique for mild hypothermia when conventional heat sources are unavailable.
Step 4: Offer warm, sweet, non-alcoholic beverages if the victim is alert and able to swallow. The sugar provides quick cellular energy for heat production, while the warm liquid directly raises core temperature. Commercial sports drinks, hot chocolate, warm juice, or simple sugar dissolved in warm water all work. Do not give alcohol or caffeine. Alcohol further impairs thermoregulation by causing vasodilation, and caffeine is a diuretic that contributes to dehydration, which compounds cold stress.
Step 5: For moderate to severe hypothermia, handle the victim with extreme gentleness. Rough movement can trigger ventricular fibrillation in a cold, irritable heart. The myocardium becomes electrically unstable below 86 °F (30 °C), and any sudden jostling can precipitate a lethal arrhythmia. Do not attempt to rewarm severely hypothermic patients in the field beyond passive insulation. These patients need active internal rewarming available only in a hospital setting — warmed intravenous fluids, heated humidified oxygen, and in extreme cases, cardiopulmonary bypass or extracorporeal membrane oxygenation.
Cold Water Immersion Hypothermia
Immersion in cold water presents a special case because water conducts heat away from the body 25 times faster than air of the same temperature. The CDC notes that sudden cold water immersion triggers an immediate gasp reflex, involuntary hyperventilation, and a spike in heart rate and blood pressure that can cause drowning even in good swimmers. This cold shock response peaks within the first two to three minutes and is the most dangerous phase.
After the initial shock, the body cools progressively. In water at 50 °F (10 °C), a person typically loses consciousness within one to two hours and can survive for a maximum of two to four hours depending on body composition, clothing, and activity level. The “1-10-1 rule” used by cold water safety organizations describes the critical timeline: one minute to control breathing and overcome the gasp reflex, 10 minutes of useful muscle function before neuromuscular cooling prevents self-rescue, and one hour before hypothermia causes loss of consciousness. Anyone rescued from cold water who appears dead should still receive aggressive resuscitation because the hypothermic state can protect the brain from hypoxic damage for extended periods — a phenomenon exploited therapeutically in targeted temperature management after cardiac arrest.
When to Call 911
Immediate emergency medical attention is required if the victim is unconscious or unresponsive, not shivering despite being very cold, has a core temperature below 90 °F (32 °C) if you have a low-reading thermometer, exhibits confusion, disorientation, or irrational behavior, or has a weak or irregular pulse. The CDC emphasizes that hypothermia can coexist with frostbite, trauma, and other cold-related injuries requiring simultaneous treatment.
What Not to Do in Hypothermia Emergencies
Equally important is knowing what to avoid. Do not give alcohol or caffeine for any reason. Do not rub or massage the victim’s arms and legs — this increases circulation to the extremities and increases the after drop effect. Do not apply direct heat such as heating pads, hot water, or a hair dryer to severely hypothermic patients. Do not assume an unconscious hypothermia victim is dead. Resuscitation efforts should continue until the person has been rewarmed to a core temperature of at least 89–93 °F (32–34 °C) unless a do-not-resuscitate order is present or injuries are clearly incompatible with life.
Prevention Strategies
Preventing hypothermia is far safer than treating it. The CDC recommends dressing in layers: a moisture-wicking base layer, an insulating middle layer, and a waterproof outer shell. Cover your head, hands, and feet in extreme cold. Avoid cotton in cold weather because it retains moisture and accelerates heat loss. Stay dry, and change out of wet clothing immediately. Avoid alcohol before or during cold exposure. Check on older neighbors and relatives during cold snaps. Keep an emergency cold-weather kit in your vehicle including blankets, extra clothing, hand warmers, non-perishable food, and a first aid kit.
FAQ
How long does it take to develop hypothermia?
The onset varies widely depending on temperature, wind chill, clothing, and individual factors. In near-freezing water, hypothermia can develop within minutes. In cold air with wet clothing, it can occur within 30–60 minutes. It may take several hours in moderately cold but dry conditions.
Can you get hypothermia indoors?
Yes. Infants, older adults, and people with certain medical conditions can develop hypothermia at indoor temperatures between 60–65 °F (15–18 °C), especially if inadequately dressed or with prolonged exposure.
Should I give someone with hypothermia alcohol?
Never. Alcohol causes vasodilation, which increases heat loss from the skin surface, and impairs judgment and shivering response. It also depresses the central nervous system, worsening confusion and the risk of unconsciousness.
What is the best way to rewarm someone with mild hypothermia?
Passive external rewarming with dry blankets, warm clothing, and a warm environment is safest. Warm sweet drinks and gentle heat packs applied to the armpits, chest, and groin are appropriate for alert patients with mild hypothermia.
How is hypothermia diagnosed in a hospital?
Medical professionals use low-reading thermometers to measure core temperature via esophageal, bladder, or rectal probes. Blood tests, ECG, and imaging may be used to assess organ function and rule out underlying causes.
Additional Resources
For more information on cold-weather emergencies and outdoor safety, read our guides on heatstroke first aid and wilderness first aid. Every outdoor enthusiast should carry the supplies listed in our first aid kit guide.
Sources: CDC Hypothermia and Cold-Related Illness Guidelines, American Red Cross First Aid/CPR Handbook, Mayo Clinic Hypothermia Overview, American Heart Association Hypothermia in Cardiac Arrest, NIH National Institute on Aging Hypothermia in Older Adults.