Hypothermia begins when your core body temperature drops below 95°F (35°C). Normal body temperature hovers around 98.6°F, so a drop of just a few degrees is enough to cross into dangerous territory. How dangerous depends on how far your temperature falls, how quickly it happens, and how fast you get warm again.
The Three Stages of Hypothermia
Hypothermia isn’t a single condition. It’s classified into three stages based on core temperature, and each stage looks and feels very different.
Mild hypothermia (90°F to 95°F / 32.2°C to 35°C) is the stage most people experience. Your body is still fighting hard to generate heat. You’ll shiver intensely, and your hands may become clumsy or numb. Thinking gets foggy, and you may struggle with coordination or slur your words. This is the stage where your body’s defenses are working at full capacity, and rewarming is relatively straightforward.
Moderate hypothermia (82.4°F to 90°F / 28°C to 32.2°C) marks a turning point. Shivering slows down or stops entirely, which is a dangerous sign: it means your body has exhausted its ability to warm itself. Confusion deepens, drowsiness sets in, and some people stop recognizing they’re in trouble. Heart rhythm can become irregular at temperatures below 86°F (30°C).
Severe hypothermia (below 82.4°F / below 28°C) is a medical emergency. At this point, the risk of a life-threatening heart rhythm called ventricular fibrillation rises significantly. Muscles stiffen, breathing becomes very slow and shallow, and consciousness fades. People in severe hypothermia can appear dead, with barely detectable vital signs, yet full recovery is sometimes possible with aggressive medical treatment.
How Your Body Loses Heat
Your body sheds heat through four pathways, and understanding them helps explain why some situations cause hypothermia faster than others.
Radiation is the biggest factor. Your body constantly emits infrared heat into the surrounding air, accounting for roughly 60% of total heat loss. This is why cold, open environments are so draining even without wind or water. Convection, the process of moving air or water carrying warmth away from your skin, handles about 15%. Wind dramatically accelerates convection, which is why wind chill matters so much. In water, convection becomes even more efficient because water pulls heat from your body far faster than air at the same temperature.
Evaporation, mainly through sweat, accounts for about 20% of heat loss at rest. Wet clothing is dangerous precisely because of this: as moisture evaporates from fabric against your skin, it strips heat with it. Conduction, the direct transfer of heat when your body touches a cold surface, contributes a smaller share (around 3%) under normal conditions. But lying on cold ground or sitting on metal changes that equation quickly.
Why Thermometers Can Be Misleading
If you suspect hypothermia, the reading on a standard home thermometer may not tell the full story. Core body temperature is what defines hypothermia, and most consumer thermometers measure surface or peripheral temperatures that consistently run lower than core readings. A 2021 systematic review found that axillary (armpit) and tympanic (ear) thermometers all underestimated true internal temperature compared to direct blood vessel measurements. Only esophageal readings showed clinically acceptable accuracy.
This matters because a forehead or underarm reading of 95°F could mean your actual core temperature is higher, or it could mean the thermometer is underreading a more serious situation. In a medical setting, rectal or esophageal temperature is used for accuracy. At home, if someone shows signs of hypothermia, treat the symptoms rather than relying on a number from a standard thermometer.
Who Is Most Vulnerable
Newborns and older adults face the highest risk, for different reasons.
Newborns have a very high surface area relative to their body size, which means they radiate heat quickly. Unlike adults, they can’t shiver to generate warmth. Instead, they rely on a specialized tissue called brown fat, located around the neck, shoulders, and kidneys, which burns calories to produce heat. This process doubles or even triples their metabolic rate and oxygen demand. If cold exposure continues unrecognized, a newborn’s body diverts calories from growth to heat production, which can impair development over time. Premature and low-birth-weight babies are at even greater risk because they have less insulating body fat and proportionally more skin surface.
Older adults lose thermoregulatory efficiency gradually. Reduced muscle mass means less shivering capacity. Thinner skin and less subcutaneous fat reduce insulation. Medications for blood pressure, depression, or anxiety can blunt the body’s cold-sensing response or impair blood vessel constriction, the mechanism that keeps warm blood near your core. Many cases of hypothermia in elderly people happen indoors, in homes that are simply too cool over extended periods.
Other high-risk groups include people who are intoxicated (alcohol dilates blood vessels near the skin, accelerating heat loss while masking the sensation of cold), those experiencing homelessness, and anyone with conditions that impair circulation or metabolism.
How Rewarming Works
Treatment depends entirely on how cold the person is. The approach changes at each stage because rewarming too aggressively can itself be dangerous.
For mild hypothermia (above roughly 93°F), passive rewarming is usually enough. This means moving to a warm environment, removing wet clothing, and wrapping in warm blankets. Your body still has the capacity to generate its own heat at this stage; it just needs help holding onto it. Warm, sweet drinks help if the person is alert enough to swallow safely.
Moderate hypothermia (roughly 86°F to 93°F) requires active external rewarming. This involves applying heat sources to the body: heated blankets, forced warm air devices, or warm packs placed on the chest, neck, and groin where large blood vessels run close to the surface. Passive methods alone won’t be enough because the body’s own heat generation has slowed too much.
Severe hypothermia (below 86°F) calls for active internal rewarming in a hospital. At this temperature, the heart is extremely irritable and vulnerable to dangerous rhythms. Medical teams use techniques that warm the blood directly, including warmed fluids circulated through the body. In cardiac arrest from severe hypothermia, resuscitation efforts may continue much longer than in other situations because cold slows cellular damage, sometimes allowing remarkable recoveries even after prolonged periods without a pulse.
Recognizing It Before It Gets Worse
The earliest signs of hypothermia are easy to dismiss: uncontrollable shivering, fumbling hands, and mild confusion. People often attribute these to simply being cold and push through. The critical warning sign is when shivering stops without the person warming up. This signals that the body has moved from fighting the cold to losing the fight.
Confusion is both a symptom and a barrier to self-rescue. As core temperature drops, judgment deteriorates. People in moderate hypothermia sometimes make paradoxical decisions, removing clothing or resisting help, because their brain is no longer processing the situation accurately. In a group setting, this means the people around someone with hypothermia may need to act on their behalf before the situation escalates.