When the human body is exposed to extreme cold, a series of physiological and biochemical responses occur in an attempt to preserve life. These responses are meant to protect vital organs and maintain a stable core temperature, but as the cold becomes more intense or prolonged, the body’s defenses begin to fail. The effects of extreme cold can range from mild discomfort to life-threatening conditions such as hypothermia and frostbite. Understanding what happens at each stage helps explain why exposure to cold is so dangerous and why quick intervention is crucial.
The human body maintains its core temperature around 37 degrees Celsius (98.6 degrees Fahrenheit). When exposed to cold, the body works to keep this temperature stable. The first line of defense is peripheral vasoconstriction, in which blood vessels near the skin’s surface narrow. This process reduces blood flow to the skin, fingers, toes, ears, and nose, helping to minimize heat loss. The redirected blood flow prioritizes the heart, lungs, and brain. While this helps maintain core temperature, it also causes the extremities to cool rapidly, which can eventually lead to frostbite if the exposure continues.
Shivering is another immediate response. It involves rapid, involuntary muscle contractions that generate heat through increased metabolic activity. During shivering, muscle activity can increase heat production up to five times the normal rate. However, shivering consumes significant amounts of energy and can only be sustained for a limited time. Once energy reserves are depleted, shivering slows or stops, which signals the beginning of a dangerous downward spiral in body temperature.
At the same time, the body’s metabolism increases slightly to generate additional heat. The release of hormones such as adrenaline and thyroid hormones stimulates this process. In extreme cold, the body also produces more brown adipose tissue, or brown fat, which burns calories to produce heat. However, these responses are limited in their ability to compensate for prolonged cold exposure. If heat loss exceeds heat production, the core temperature begins to fall.
As body temperature drops below 35 degrees Celsius (95 degrees Fahrenheit), hypothermia begins. In the early stages, a person may feel intense cold, shiver uncontrollably, and experience numbness in the hands and feet. Cognitive functions start to decline, and coordination becomes impaired. Simple tasks like buttoning a coat or lighting a fire become difficult. The person may appear clumsy or confused, and speech can become slurred. The body is still trying to preserve heat, but it is losing the battle.
When the core temperature falls further, typically below 33 degrees Celsius (91 degrees Fahrenheit), mental confusion deepens. The brain, which depends on precise temperature regulation, becomes increasingly sluggish. People in this stage may behave irrationally, sometimes removing clothing despite the cold. This paradoxical undressing occurs because of nerve malfunction and false sensations of heat. Muscles stiffen, reaction times slow, and breathing becomes shallower. The pulse weakens, and blood pressure drops as the heart struggles to maintain circulation.
If the temperature continues to drop below 30 degrees Celsius (86 degrees Fahrenheit), the situation becomes critical. The body’s automatic responses begin to fail. Shivering stops completely, signaling that energy reserves are exhausted. The person becomes lethargic, often losing consciousness. The heart rate and breathing slow dramatically, and the risk of cardiac arrhythmias increases. The brain’s electrical activity decreases, and without medical intervention, the person can die from cardiac arrest or respiratory failure.
Extreme cold also affects the blood and cellular function. As temperature decreases, blood becomes thicker and flows more slowly. This can lead to reduced oxygen delivery to tissues, compounding the damage caused by low temperatures. The cold also slows enzyme activity, disrupting metabolism and energy production. Cells become dehydrated as water moves out of them to form ice crystals in the surrounding tissue. In localized areas such as fingers, toes, or the nose, this leads to frostbite.
Frostbite occurs when tissue freezes. Ice crystals form inside and around cells, damaging their structure. Blood flow to the area stops, and the lack of oxygen causes cell death. In mild frostbite, the skin may appear red and feel numb or prickly. In more severe cases, the skin turns pale or bluish, hardens, and may eventually blister. If the tissue is completely frozen, it can become black and die, requiring amputation. Rewarming must be done carefully to prevent further injury, as thawing too quickly can rupture cell membranes and cause additional tissue loss.
Beyond the physical effects, extreme cold also influences mental state and decision-making. As the brain cools, it becomes less able to process information. Memory, attention, and reasoning deteriorate. In some cases, individuals become passive or even euphoric, unaware of their worsening condition. This cognitive decline often prevents people from seeking shelter or help, which is why hypothermia can progress so quickly and fatally in outdoor environments.
If a person is rescued and warmed in time, the body can recover, but the process must be handled carefully. Rapid rewarming of the core is essential to prevent further complications such as shock or arrhythmia. Blood warmed too quickly in the limbs can rush back to the core, bringing cold, acidic blood that can further strain the heart. Medical rewarming often involves warm fluids, heated blankets, and in severe cases, extracorporeal warming using specialized machines.
Even after recovery, long-term effects can persist. Nerve damage, chronic pain, and sensitivity to cold are common in those who have suffered frostbite or severe hypothermia. The heart, kidneys, and other organs may also experience lasting effects due to the stress of reduced blood flow and oxygen deprivation.
In summary, extreme cold triggers a complex cascade of physiological responses designed to protect the core temperature. The body constricts blood vessels, shivers, and increases metabolism to generate and conserve heat. However, when these measures fail, hypothermia and frostbite set in, progressively impairing muscle coordination, mental function, and vital organ performance. Without timely warming and medical care, the body’s systems shut down completely. Extreme cold is therefore one of nature’s most formidable threats, capable of overwhelming even the strongest human defenses if exposure lasts too long.