Hypothermia happens when your body loses heat faster than it can produce it, dropping your core temperature below 95°F (35°C). While most people associate it with extreme cold, hypothermia can develop in surprisingly mild conditions when other factors stack up: wet clothing, certain medications, alcohol, or an underlying health condition that weakens your body’s ability to regulate temperature.
How Your Body Loses Heat
Your body constantly generates heat through metabolism and preserves it by narrowing blood vessels near the skin, keeping warm blood closer to your vital organs. When that system is overwhelmed or impaired, your core temperature drops. The process works through four basic pathways: conduction (direct contact with something cold), convection (wind pulling heat from your skin), radiation (body heat escaping into cooler surroundings), and evaporation (moisture on your skin or clothing drawing heat as it dries).
Understanding these pathways explains why some situations are far more dangerous than others. Cold water, for example, conducts heat away from the body roughly 20 to 25 times faster than air at the same temperature. A person submerged in cold water can become hypothermic within minutes, while someone in cold air of the same temperature might last hours. Wet clothing works similarly, absorbing body heat and increasing both conductive and evaporative losses. Even a light rain on a cool, windy day can create conditions where hypothermia becomes a real threat.
Cold Exposure and Environmental Causes
The most obvious cause is prolonged exposure to cold air, cold water, or both. But “cold” doesn’t have to mean subzero. Hypothermia can occur at temperatures well above freezing, particularly when wind and moisture are involved. Hikers caught in unexpected rain at 50°F with a strong wind are a classic scenario. Wind strips the thin layer of warmed air your body maintains near the skin, dramatically accelerating heat loss.
Cold water immersion is especially dangerous because the thermal conductivity of water is roughly 24 times that of air. Falls into lakes, rivers, or the ocean can cause rapid, life-threatening drops in core temperature. Even strong swimmers lose coordination and muscle control quickly as their body temperature falls, which is why drowning and hypothermia are closely linked in cold water incidents. People who survive the initial shock may still face hypothermia that progresses over minutes rather than hours.
Indoor hypothermia is more common than many people realize. Poorly heated homes during winter, especially among older adults living alone, account for a significant share of hypothermia cases. A house at 60°F might feel merely uncomfortable to a healthy younger person, but it can slowly lower core temperature in someone with reduced metabolic heat production.
Alcohol and Recreational Drugs
Alcohol is one of the most well-known contributors to hypothermia, but the reason it’s dangerous isn’t quite what most people think. The common explanation is that alcohol dilates blood vessels near the skin, letting heat escape faster. While that does happen (and creates the misleading sensation of warmth), research shows the primary mechanism is actually different. Alcohol impairs the shivering response, largely by causing blood sugar to drop. Shivering is your body’s most powerful emergency heat-generating tool, and when it’s suppressed, core temperature falls much more quickly.
Alcohol also clouds judgment. People who are intoxicated are more likely to stay outside in cold weather, fall asleep in exposed locations, or fail to notice early warning signs like intense shivering and numbness. Recreational drugs that cause sedation carry similar risks, reducing awareness and physical responses to cold.
Medications That Impair Temperature Regulation
Several common prescription medications interfere with your body’s ability to sense or respond to cold. These don’t cause hypothermia on their own, but they lower the threshold, meaning it takes less cold exposure to push you into dangerous territory.
- Antipsychotics can interfere with the brain’s central temperature control system, disrupting the signals that trigger shivering and blood vessel constriction.
- Beta blockers, used for high blood pressure and heart conditions, reduce the body’s ability to constrict blood vessels near the skin. They can also lower blood pressure in ways that increase vulnerability.
- Sedatives and opioids reduce awareness of cold and impair the physical responses needed to seek warmth or shelter.
- Anticholinergic drugs and tricyclic antidepressants interfere with sweating and central thermoregulation, disrupting the feedback loop your body relies on to maintain a stable temperature.
- SSRIs and SNRIs, commonly prescribed for depression and anxiety, can also alter the body’s cooling and heating responses.
If you take any of these medications and spend time outdoors in cold weather, or live in a home that isn’t well heated, it’s worth being aware of this added vulnerability. The risk increases when multiple medications are combined.
Medical Conditions That Weaken Heat Production
Certain health conditions directly impair the body’s ability to generate or conserve heat, making hypothermia possible even in mildly cool environments.
Severe hypothyroidism is one of the most significant. Thyroid hormone drives your metabolism, which is your body’s primary source of internal heat. When thyroid function drops severely, metabolic heat production slows across nearly every body system. In its most extreme form, called myxedema coma, the body essentially begins shutting down, and core temperature can fall dangerously low. Infections like pneumonia can trigger this crisis in people with existing thyroid disease.
Diabetes can contribute to hypothermia in multiple ways. Poor circulation reduces the delivery of warm blood to the extremities, and nerve damage (a common complication) can impair the ability to sense cold. Low blood sugar itself reduces the fuel available for heat generation, and severe episodes can mimic or accelerate hypothermia.
Sepsis, a body-wide response to severe infection, can paradoxically cause hypothermia rather than fever. When the immune system’s response overwhelms the body’s resources, core temperature may drop rather than rise, particularly in older adults or people with weakened immune systems.
Brain Injuries and Nervous System Damage
Your body’s thermostat lives in a small region of the brain called the hypothalamus. This area continuously monitors your core temperature and triggers responses like shivering, blood vessel constriction, and behavioral changes (the urge to put on a coat, for instance). When the hypothalamus is damaged, those automatic responses can fail entirely.
Traumatic brain injuries, strokes, and brain tumors can all disrupt this system. The damage doesn’t have to be directly to the hypothalamus itself. Any injury that interferes with the flow of sensory information (temperature signals from the skin and body) or the motor output (the commands to shiver or constrict blood vessels) can leave someone unable to respond appropriately to cold. People with spinal cord injuries face a similar challenge, as the nerve pathways carrying temperature signals and shivering commands may be severed or impaired.
Why Infants and Older Adults Are Most Vulnerable
Newborns, especially premature infants, lose heat rapidly because of their large surface area relative to their body mass. A small body with proportionally more skin exposed to the environment radiates heat much faster than an adult’s. Premature infants are at particular risk because they have less brown fat, a specialized tissue packed with blood vessels that generates heat by burning energy. Full-term babies have deposits of brown fat around the neck, shoulders, and kidneys that activate when their temperature dips below about 97.7°F, but preterm infants have significantly less of this insulation. Their naturally extended posture also exposes more skin to the surrounding air compared to the curled position of a full-term newborn.
Older adults face a different set of problems. Research comparing elderly and younger adults during controlled cooling found that older subjects had lower baseline metabolic heat production and a significantly weaker blood vessel constriction response in their extremities. In practical terms, older adults maintained much higher blood flow to their fingertips during cold exposure, meaning heat was escaping from the very areas designed to shut down circulation first. Their shivering response also kicked in later, at a lower core temperature, giving the cold a head start. While younger subjects in the same study were able to maintain their core temperature throughout the cooling period, elderly subjects showed a progressive decline, dropping nearly 0.4°F below baseline before shivering even began.
These biological changes mean an older person may not feel as cold as they should, may not shiver as early as they need to, and may lose heat from their hands and feet without the usual protective constriction. Combined with the medications many older adults take and the possibility of living in under-heated homes, the risk adds up quietly.
The Three Stages of Hypothermia
Hypothermia progresses through three recognized stages, and knowing the signs of each matters because the earlier it’s caught, the easier it is to reverse.
Mild hypothermia (95°F to 89.6°F) produces intense shivering, clumsiness, slurred speech, and confusion. Your body is still actively fighting to generate heat, and rewarming with dry clothing, blankets, and a warm environment is usually effective. Moderate hypothermia (below 89.6°F to 82.4°F) is more dangerous. Shivering may actually stop, which is a bad sign: it means the body is losing the ability to generate its own heat. Confusion deepens, drowsiness sets in, and heart rhythm can become irregular. Severe hypothermia (below 82.4°F) is life-threatening. The person may appear unconscious or even dead, with a barely detectable pulse and very slow breathing.
One important phenomenon during rewarming is called “afterdrop,” where core temperature continues to fall briefly even after warming begins. This happens because cold blood from the extremities circulates back to the core as blood vessels reopen. It’s one reason why rewarming someone with moderate or severe hypothermia needs to happen gradually and, ideally, with professional medical support rather than aggressive external heating alone.