Exposure to extreme cold can lead to two distinct types of injury: frostbite and hypothermia. Frostbite is a localized injury involving the freezing of tissues in extremities, whereas hypothermia is a systemic condition where the body’s entire core temperature drops to a dangerously low level. Understanding the difference between these two cold-weather emergencies is the first step toward effective prevention and appropriate response.
Fundamental Mechanisms and Affected Systems
Frostbite is initiated by the body’s natural response to cold: peripheral vasoconstriction. This process narrows blood vessels in the extremities, such as the fingers, toes, ears, and nose, to shunt warm blood toward the vital internal organs. As blood flow decreases in the exposed tissues, their temperature drops until ice crystals begin to form in the extracellular space, which typically occurs below 31°F (-0.55°C).
The formation of these ice crystals causes mechanical damage to cell membranes and draws water out of the cells, leading to severe cellular dehydration. Following the initial freezing, the injury progresses due to microvascular damage, where blood clots (thrombi) form within the small vessels, causing prolonged ischemia. This leads to progressive tissue death and necrosis.
Hypothermia, by contrast, is a failure of the body’s thermoregulation system, resulting in a core body temperature below 95°F (35°C). The body loses heat faster than it can produce it, overwhelming the initial defensive mechanisms like shivering and vasoconstriction. This systemic cooling affects the central nervous system (CNS) and the cardiovascular system.
As the core temperature decreases, metabolic activity slows down, progressively depressing CNS function. The heart is highly sensitive to the drop in temperature, which can slow the electrical conduction and lead to heart rhythm abnormalities, such as ventricular fibrillation, which may occur at temperatures below 82.4°F (28°C). Unlike frostbite, hypothermia is not defined by tissue freezing but by the failure of the entire organism to maintain thermal balance.
Distinct Clinical Presentations and Warning Signs
The signs of frostbite are localized, starting with a mild presentation known as frostnip, where the skin appears pale or red and is accompanied by tingling or numbness. As the injury deepens, the skin becomes waxy, hard, and may appear white, grayish-yellow, or even blue. A complete loss of sensation in the affected area is a hallmark of significant frostbite.
Upon rewarming, more severe frostbite can manifest as swelling and the formation of blisters, which may be clear or filled with blood, indicating deeper tissue involvement. In the most severe cases, the tissue becomes hard and cold to the touch and eventually turns black, a clear sign of tissue necrosis.
Hypothermia presents with systemic symptoms that progress from mild to severe. In the initial stage (mild, 90–95°F), the body attempts to generate heat through shivering. The person may still be alert but will exhibit mild confusion and impaired coordination.
As the core temperature falls further (moderate, 82–90°F), shivering often ceases entirely, indicating the body’s heat-generating mechanisms are failing. At this point, confusion worsens, and the individual may become lethargic and drowsy. In severe hypothermia (below 82°F), the victim may lose consciousness, breathing becomes very slow and shallow, and the pulse weakens significantly, risking cardiac arrest.
Immediate First Aid and Emergency Response
The first aid response for frostbite focuses on gentle rewarming and preventing further damage to the localized tissue. The affected person should be moved to a warm environment. Avoid rubbing the injured area, as this can cause mechanical damage to the tissue.
To rewarm the frostbitten area, it should be immersed in warm water, ideally between 104°F and 108°F (40°C–42°C), for about 30 minutes. Direct dry heat sources like radiators or fires must be avoided because the skin is numb and can easily be burned. Rewarming should only be attempted if there is no risk of the tissue refreezing before reaching medical care, as a cycle of freezing and thawing dramatically worsens the injury.
For hypothermia, the immediate priority is minimizing further heat loss. Wet clothing must be removed immediately and replaced with dry layers or blankets to insulate the body. Gentle handling is necessary because rough movement can trigger cardiac arrhythmias in a severely hypothermic heart.
If the person is conscious, offering warm, non-alcoholic, and non-caffeinated fluids can help raise the core temperature. Warm compresses should be applied only to the core areas of the body—the neck, chest wall, and groin—to prevent the phenomenon known as “core temperature after-drop.” This after-drop occurs when cold blood from the extremities rushes back to the core upon peripheral warming, causing a sudden drop in internal temperature. All moderate to severe cases of hypothermia require immediate emergency medical services.