The human body maintains a stable internal temperature, a process called thermoregulation. When environmental temperatures drop too low, or other factors exacerbate heat loss, the body’s defenses can be overwhelmed, leading to dangerous conditions. Understanding these limits involves recognizing the body’s natural responses to cold and the specific physiological impacts of extreme temperatures.
How the Body Regulates Temperature
The body’s core temperature is around 37 degrees Celsius (98.6 degrees Fahrenheit). To maintain this, the brain’s hypothalamus acts as a thermostat, sensing temperature changes and initiating responses. When exposed to cold, the body first attempts to conserve heat. Vasoconstriction, where blood vessels near the skin’s surface narrow, reduces blood flow and heat loss from the skin.
If heat conservation is insufficient, the body increases heat production. Shivering, the rapid, involuntary contraction and relaxation of muscles, generates heat through increased metabolic activity. These responses are effective within limits. However, prolonged or severe cold exposure can push these systems beyond their capacity.
Defining Dangerous Cold Temperatures
When the body loses heat faster than it can produce it, core temperature begins to drop, leading to a condition called hypothermia. Hypothermia is defined as a core body temperature below 35.0 degrees Celsius (95.0 degrees Fahrenheit). The severity of hypothermia is categorized into stages, each with specific temperature ranges and symptoms.
Mild hypothermia occurs when the core temperature falls between 32 and 35 degrees Celsius (90-95 degrees Fahrenheit). Symptoms include shivering, mental confusion, slurred speech, and increased urination. As the body temperature drops further to between 28 and 32 degrees Celsius (82-90 degrees Fahrenheit), moderate hypothermia sets in, characterized by the cessation of shivering, increased confusion, and impaired coordination. Severe hypothermia, with a core temperature below 28 degrees Celsius (82 degrees Fahrenheit), can lead to unconsciousness, muscle rigidity, and risk of cardiac arrest.
Factors Intensifying Cold’s Impact
Air temperature is not the sole determinant of how cold a person feels or the risk of cold injury. Several environmental and individual factors can accelerate heat loss and intensify the impact of cold. Wind chill, for instance, describes how wind increases the rate at which heat is drawn away from exposed skin, accelerating heat loss from the body’s surface.
Moisture, whether from rain, sweat, or immersion in cold water, increases heat conduction away from the body. Water conducts heat faster than air, making wet conditions dangerous. Duration of exposure also matters; the longer a person is exposed to cold conditions, the greater the risk of hypothermia and other cold-related injuries. Individual factors influencing a person’s vulnerability to cold include:
Age
Health conditions (like cardiovascular issues or diabetes)
Fatigue
Dehydration
Body composition
Physical Harms of Extreme Cold
When the body’s temperature regulation fails, or tissues are directly exposed to extreme cold, physical harms can occur. Frostbite is a localized freezing injury to body tissues, affecting extremities like fingers, toes, ears, and the nose. It occurs when temperatures drop below 0 degrees Celsius (32 degrees Fahrenheit), causing ice crystals to form within cells and damage tissues.
Frostbite can range from superficial, involving only the skin surface, to deep, affecting underlying tissues, muscles, and bones. Symptoms include numbness, waxy or grayish skin, and blistering, potentially leading to permanent tissue damage, infection, or even amputation.
Beyond localized injury, hypothermia can lead to systemic organ failure. As core temperature drops, the brain’s function becomes impaired, causing confusion, disorientation, and eventually loss of consciousness. The heart can develop irregular rhythms, progressing to cardiac arrest, and the respiratory system slows, leading to shallow or absent breathing. This systemic shutdown ultimately results in death if not promptly reversed.