Hypothermia begins when your core body temperature drops below 95°F (35°C). Normal body temperature sits around 98.6°F (37°C), so it only takes a drop of about 3.5 degrees to cross into dangerous territory. What surprises most people is that hypothermia doesn’t require extreme cold. It can happen at air temperatures well above freezing, especially if you’re wet, exhausted, or sitting still for a long time.
The Three Stages of Hypothermia
Hypothermia is classified by how far your core temperature has fallen, and each stage looks and feels different.
Mild (90°F to 95°F / 32°C to 35°C): This is the stage most people experience. Your body ramps up shivering to generate heat. You’ll notice clumsiness, difficulty thinking clearly, and slurred speech. Your hands may become too numb to do simple tasks like zipping a jacket. Many people don’t recognize these symptoms in themselves because the cold is already affecting their judgment.
Moderate (82.4°F to 90°F / 28°C to 32°C): Shivering becomes violent, then may start to weaken. Confusion deepens. Drowsiness sets in, and some people stop trying to warm themselves or even feel paradoxically warm. Muscles stiffen, and coordination deteriorates further.
Severe (below 82.4°F / 28°C): Shivering stops entirely. This is a critical warning sign, not a sign of improvement. At this point, the body has essentially exhausted its ability to rewarm itself. Loss of consciousness, weak pulse, and dangerously slow breathing follow. Without medical intervention, the heart can stop.
How Your Body Loses Heat
Your body sheds heat through four main pathways, and understanding them explains why some situations are far more dangerous than others.
Radiation accounts for roughly 65% of your body’s heat loss. Heat simply radiates off your skin into cooler air, the same way a wood stove warms a room. This process kicks in at air temperatures below about 68°F (20°C), which is why even mild conditions can slowly drain your warmth if you’re not dressed for them.
Convection, the cooling effect of wind, is responsible for 10% to 15% of heat loss. Wind strips away the thin layer of warm air that sits against your skin. This is the principle behind wind chill: a 35°F day with a 30 mph wind can cool your body as fast as a much colder, calm day.
Conduction transfers heat through direct contact with cold surfaces or materials. In still air, conduction only accounts for about 2% of heat loss. But water changes the equation dramatically. Cold water pulls heat from your body far faster than cold air does, which is why falling into cold water or wearing wet clothing is so dangerous. Wet clothes cling to your skin and accelerate heat loss through both conduction and evaporation simultaneously.
Evaporation rounds out the picture. Sweat or rain on your skin absorbs heat as it dries. In dry, windy weather, evaporative heat loss increases significantly, compounding the cooling effects of convection.
You Don’t Need Freezing Temperatures
One of the most common misconceptions is that hypothermia only happens in extreme winter conditions. In reality, most cases occur at air temperatures between 30°F and 50°F, often combined with rain, wind, or physical exhaustion. Hikers caught in a cool rain on a windy autumn day are classic hypothermia candidates, even when the temperature is well above freezing.
Hypothermia can even happen indoors. Indoor temperatures as mild as 60°F to 65°F can trigger hypothermia over an extended period, particularly in older adults or anyone who is sedentary. People living in poorly heated homes during winter are at genuine risk, especially if they’re sitting or sleeping for long stretches without enough blankets or warm clothing.
Why Some People Are More Vulnerable
Infants lose heat much faster than adults. A baby’s head makes up over 20% of their total body surface area, compared to roughly 10% in adults. Leaving an infant’s head uncovered in cool conditions can drain their body heat surprisingly fast. Small children face similar risks because of their high surface-area-to-body-mass ratio.
Older adults are vulnerable for different reasons. Aging reduces the number of nerve endings in the skin, making it harder to notice when you’re getting cold. Older people also tend to have less body fat (which acts as insulation) and a lower metabolic rate, meaning they generate less internal heat. An elderly person can be sitting in a cool room and not realize their core temperature is gradually falling.
Why Alcohol Makes It Worse
Alcohol creates a convincing but dangerous illusion of warmth. When you drink, your blood vessels dilate, sending more blood to the surface of your skin. You feel a flush of warmth, but what’s actually happening is the opposite of helpful: blood near the skin’s surface loses heat rapidly to the surrounding air. Your body’s core temperature drops faster, even as you feel warmer.
This is a double problem. Alcohol tricks you into thinking you’re fine while simultaneously accelerating heat loss from your core, heart, and vital organs. It also impairs judgment, making you less likely to seek shelter or recognize early symptoms of hypothermia.
What to Do If Someone Is Hypothermic
Move the person out of the cold gently. Rough handling or sudden movements can stress a cold heart. If you can’t get indoors, shield them from the wind, especially around the head and neck, and insulate them from the ground with a blanket, backpack, or anything available. Remove wet clothing and replace it with dry layers or blankets.
Focus rewarming efforts on the center of the body: the neck, chest, and groin. Warm, dry compresses, an electric blanket, or a towel-wrapped hot water bottle all work. Offer warm, sweet, nonalcoholic drinks if the person is conscious and able to swallow.
There are important things to avoid. Don’t try to warm the arms and legs directly. Heating the extremities can push cold blood back toward the heart too quickly, which can trigger dangerous heart rhythms. Don’t offer alcohol, which slows rewarming, or cigarettes, which constrict blood vessels and reduce circulation to areas that need it most. For moderate or severe hypothermia, get emergency medical help as quickly as possible while keeping the person warm and still.