Hypothermia is a medical emergency where the body loses heat faster than it can produce it, leading to a dangerously low core body temperature. It is defined as a core body temperature below 95 degrees Fahrenheit (35 degrees Celsius). This condition can affect the brain, nervous system, and other organs, impairing their function. If left untreated, hypothermia can cause the heart and respiratory system to fail, potentially leading to death.
Understanding Core Body Temperature
Core body temperature refers to the temperature of the body’s vital internal organs, which remains stable around 98.6 degrees Fahrenheit (37 degrees Celsius). The human body has a system called thermoregulation, controlled by the hypothalamus in the brain, which acts like a thermostat to maintain this consistent temperature.
The body balances heat production and heat loss. Heat is generated through metabolic processes and muscle activity, like shivering. Heat can be lost through several mechanisms. Radiation involves heat radiating from the skin to the environment, while convection occurs when warm air rises and is replaced by cooler air. Evaporation of sweat from the skin removes heat, and conduction involves heat transfer through direct contact with a cooler object or surface.
Levels of Hypothermia and Their Signs
Hypothermia progresses through distinct stages, each marked by specific temperature ranges and escalating symptoms. Recognizing these signs is important for timely intervention.
Mild Hypothermia
Mild hypothermia occurs when the core body temperature falls to between 95 and 89.6 degrees Fahrenheit (35 to 32 degrees Celsius). The body tries to rewarm itself, often leading to uncontrollable shivering. Other signs include pale and cool skin, numbness in the extremities, and increased heart rate and breathing. Individuals may exhibit sluggish responses, drowsiness, lethargy, confusion, impaired judgment, slurred speech, and clumsiness.
Moderate Hypothermia
As the body temperature continues to drop, entering the moderate hypothermia range of 89.6 to 82.4 degrees Fahrenheit (32 to 28 degrees Celsius), shivering stops. This cessation of shivering can be a deceptive sign, as it indicates a worsening of the condition. The individual’s conscious state decreases, and confusion becomes more pronounced.
Physical signs include a slowed heart rate, reduced breathing rate, and low blood pressure. Pupils may become enlarged and less responsive to light. Muscle stiffness can increase, and paradoxical undressing—where a person removes clothing despite the cold—may occur.
Severe Hypothermia
Severe hypothermia is a life-threatening stage, occurring when the core body temperature drops below 82.4 degrees Fahrenheit (28 degrees Celsius). The individual is unconscious and unresponsive. Shivering has ceased entirely, and muscle rigidity is present.
The heart rate and breathing become extremely slow, and blood pressure drops low. Reflexes may be completely absent, and pupils can be dilated and fixed. In the most severe cases, the person may appear to have no vital signs, mimicking death, and cardiac arrest is a high risk.
Causes and Vulnerabilities
Hypothermia results from the body losing heat faster than it can generate it, and various factors can contribute to this imbalance. The most common cause is prolonged exposure to cold environmental conditions, including cold weather, wet clothing, or immersion in cold water. Even moderate temperatures can lead to hypothermia if exposure is lengthy or if clothing is wet. For instance, falling into cold water can cause a rapid drop in body temperature because water conducts heat away from the body more quickly than air.
Individual vulnerabilities also increase the risk of developing hypothermia. Both infants and older adults are more susceptible; infants lose heat faster than adults, and older individuals may have a diminished ability to regulate body temperature and sense cold. Medical conditions such as hypothyroidism, diabetes, and stroke can impair the body’s heat production or lead to immobility, increasing risk. Substance use, particularly alcohol, is an important factor, as alcohol causes blood vessels to dilate, making a person feel warm while actually accelerating heat loss. Medications, mental health conditions like dementia, and exhaustion can also compromise judgment and the body’s ability to respond to cold, increasing the risk.
Emergency Response and Recovery
Immediate action is necessary when hypothermia is suspected. The first step is to call 911 or your local emergency number for professional medical assistance. While waiting for help, gently move the person to a warm, dry environment, such as indoors or into a heated vehicle, if possible. If moving indoors is not an option, shield the individual from wind and insulate them from the cold ground by placing blankets or coats underneath them.
Carefully remove any wet clothing, as it rapidly draws heat away from the body, and replace it with dry, warm blankets or coats. Focus on warming the center of the body—the neck, chest, and groin—using warm, dry compresses or an electric blanket, if available. Avoid applying direct extreme heat, such as hot water or heating lamps, and do not rub or massage the person’s limbs, as this can force cold blood back to the core and stress the heart. If the person is alert and able to swallow, offer warm, sweet, non-alcoholic, and non-caffeinated drinks to help raise their body temperature. Continuously monitor their breathing and pulse, and if they stop breathing or show no signs of life, begin cardiopulmonary resuscitation (CPR) immediately if you are trained.
In a hospital setting, medical interventions may include heated intravenous fluids, warmed humidified oxygen through a mask, or blood rewarming, where blood is drawn, warmed externally, and then recirculated. The recovery process depends on the severity and duration of hypothermia, with milder cases often recovering fully with rewarming, while severe cases may require extensive medical support and can have lasting complications.
Preventing Hypothermia
Taking steps can reduce the risk of hypothermia. Dressing in layers is an effective strategy, as it traps air, creating an insulating barrier against the cold. The inner layer should wick sweat away from the skin, while middle layers provide insulation, and the outer layer should be wind and water-resistant.
Staying dry is equally important, as wet clothing loses most of its insulating value, accelerating heat loss. Wear a warm hat, as much body heat can be lost through the head, along with gloves or mittens and warm, waterproof footwear. Maintaining good nutrition and hydration by eating regular, balanced meals and drinking plenty of fluids provides the body with the necessary energy to generate heat. Limiting alcohol and caffeine intake in cold conditions is advisable, as these substances can interfere with the body’s ability to retain heat.