Preventing hypothermia comes down to one principle: keep your body producing heat faster than it loses heat. Your core temperature only needs to drop a few degrees, from the normal 98.6°F to 95°F, for hypothermia to set in. That can happen faster than most people expect, especially in wet or windy conditions, and the early signs are easy to miss.
How Your Body Loses Heat
Heat leaves your body through four main routes, and understanding them helps you block each one. Radiation is heat escaping directly from exposed skin into the surrounding air. Convection is wind or water stripping warmth away from your skin’s surface. Conduction is heat transferring into anything cold you’re touching, like the ground, a metal railing, or water. Evaporation pulls heat from your body as sweat or moisture dries off your skin.
In calm, cool air, radiation and convection account for the bulk of your heat loss. Wind dramatically accelerates convective loss, which is why a 40°F day with strong wind can be more dangerous than a still 25°F day. Water conducts heat away from your body roughly 25 times faster than air at the same temperature, making wet clothing or cold water immersion the fastest path to hypothermia. Every prevention strategy targets one or more of these pathways.
Dress in Layers, Not Bulk
Layering works because trapped air between fabric layers acts as insulation. Three layers cover the basics: a moisture-wicking base layer against your skin, an insulating middle layer (fleece, down, or synthetic fill), and a wind- and water-resistant outer shell. The base layer matters more than people realize. Cotton absorbs moisture and holds it against your skin, accelerating evaporative and conductive heat loss. Wool and synthetic fabrics wick sweat away and retain insulating ability even when damp.
Your head, neck, and hands lose heat disproportionately because blood vessels run close to the surface. A hat, neck gaiter, and insulated gloves are not optional in cold conditions. If you start sweating, open a zipper or remove a layer before the moisture builds up. Wet insulation is barely better than no insulation.
Stay Dry at All Costs
Wet clothing is the single most common contributor to hypothermia outside of cold water immersion. Rain, snow, sweat, and stream crossings all create the same problem: water against skin pulls heat away rapidly through both conduction and evaporation. If your clothes get wet, changing into dry layers is the highest priority, more urgent than building a fire or setting up shelter.
Waterproof outer layers help, but so does pacing yourself. Overexertion in cold weather produces sweat that soaks your base layer from the inside. If you’re hiking, skiing, or working outdoors, moderate your effort to stay warm without drenching your clothing. Carry extra dry socks and a base layer in a waterproof bag as a baseline precaution.
Block Wind and Ground Contact
Wind strips your body’s thin layer of warmed air, resetting conductive loss with every gust. A windproof outer shell handles this during activity. If you stop moving, get behind a natural windbreak, inside a vehicle, or into a shelter. Even a simple tarp angled against the wind makes a measurable difference.
Sitting or lying directly on cold ground drains heat through conduction. Use a foam sleeping pad, a layer of dry leaves, a backpack, or anything that creates a barrier between your body and the ground. This matters especially at rest or during sleep, when your metabolic heat production drops.
Eat Carbohydrates and Drink Warm Fluids
Your body generates heat through metabolism, and shivering can burn through energy reserves quickly. The body prefers carbohydrates to fuel shivering, and carbs convert to usable energy faster than fat or protein. Trail mix, energy bars, crackers, chocolate, and sugary drinks all work. In sustained cold exposure, eating small amounts frequently keeps your internal furnace running.
Warm drinks help, but the calorie content matters more than the temperature. A hot cup of sugary tea provides meaningful calories along with a brief warming sensation. Plain hot water feels good but contributes little to your thermal balance. The key is to keep eating and drinking before you feel desperate, because by the time shivering is intense, your glycogen stores may already be depleted.
Why Alcohol Makes Things Worse
Alcohol creates a convincing illusion of warmth while actually increasing your risk. It causes blood vessels near the skin to dilate, sending warm blood to your extremities. This produces a flush of heat across your skin that feels reassuring but accelerates heat loss from your core. Research suggests alcohol also lowers your body’s internal temperature set point, meaning your thermoregulatory system becomes less aggressive about defending your core temperature.
On top of that, alcohol impairs judgment, making you less likely to recognize early hypothermia symptoms or take protective action. It also acts as a diuretic, contributing to dehydration, which further compromises your body’s ability to regulate temperature. In cold conditions, avoid alcohol entirely.
Recognize the Early Warning Signs
Hypothermia is easiest to prevent and reverse when caught early, but the early signs are subtle enough that the person affected often doesn’t notice them. Shivering is the body’s automatic defense, an attempt to generate heat through rapid muscle contraction. It’s the clearest early signal that core temperature is dropping.
Beyond shivering, watch for what outdoor professionals call “the umbles”: stumbling, mumbling, fumbling, and grumbling. Clumsiness and poor coordination appear as fine motor skills decline. Speech becomes slurred. Thinking gets foggy, and the person may become irritable or withdrawn. These signs indicate mild hypothermia, with core temperature between roughly 90°F and 95°F. At this stage, the person can still rewarm themselves with dry clothing, shelter, food, and warmth.
As core temperature drops below 90°F into moderate hypothermia, coordination worsens, alertness decreases, and decision-making deteriorates sharply. Shivering may still be present but grows less reliable. Below about 82°F, shivering stops entirely, consciousness fades toward coma, and the heart becomes dangerously unstable. At that point, field rewarming alone is not enough.
What to Do if Someone Is Already Cold
The first step in field rewarming is stopping further heat loss. Get the person out of wind and rain. Remove wet clothing and replace it with dry layers. If dry clothing isn’t available, wring out what they’re wearing and add a windproof and waterproof outer layer like a tarp or emergency blanket to block evaporative and convective losses.
Wrap the person in insulation and place heat sources against the chest and armpits, where major blood vessels run close to the surface. Hot water bottles and larger chemical heat packs work for this. Small hand warmers, however, do not produce enough heat to meaningfully raise core temperature. Skin-to-skin contact inside a sleeping bag is another effective option. If the person is alert and able to swallow safely, give them warm, sweet drinks and high-calorie food.
Handle a moderately or severely hypothermic person gently. Rough movement or suddenly standing them upright can trigger dangerous heart rhythms or a further drop in core temperature as cold blood from the extremities rushes to the core. Keep them horizontal and move them as little as necessary. Do not put them in a warm shower or bath, as rapid peripheral warming can cause blood pressure to drop sharply.
Cold Water Creates Unique Danger
Falling into cold water is the most dangerous hypothermia scenario because water conducts heat so efficiently. Core temperature can drop to dangerous levels in minutes rather than hours. If you fall in, resist the urge to swim aggressively. Pull your knees to your chest to protect your core and minimize the surface area exposed to water. If you’re with others, huddle together.
Get out of the water as quickly as possible, even if the air temperature is also cold. Air is a far less efficient conductor of heat. Once out, follow the same protocol: strip wet clothing, insulate, block wind, and apply heat to the core. People pulled from cold water need to be kept horizontal, as the sudden shift to an upright position can cause cardiovascular collapse.
Plan Ahead for Cold Exposure
Most hypothermia cases aren’t mountaineering disasters. They happen during day hikes that take longer than expected, car breakdowns in winter, or afternoons on the water when conditions change. Preparation is the most effective prevention. Check the forecast, including wind chill. Carry extra dry layers, a windproof emergency blanket or bivy, high-calorie snacks, and a way to make fire or heat water. Tell someone where you’re going and when you’ll be back.
Pay extra attention to anyone in your group who is thin, elderly, very young, exhausted, or injured. These factors all reduce the body’s ability to generate and retain heat. Children lose heat faster due to their higher surface-area-to-body-mass ratio. Fatigue depletes the glycogen stores that fuel shivering. An injury that limits mobility removes the heat generated by physical activity. Checking on the most vulnerable members of your group is one of the simplest and most effective prevention strategies there is.