Cold exposure presents a significant threat to human health. The body’s response to severe cold can manifest in two distinct, yet often confused, conditions: frostbite and hypothermia. While both result from being exposed to low temperatures, they differ fundamentally in how they affect the body. Understanding the mechanisms and symptoms of each injury is crucial for proper recognition and immediate action.
Frostbite: A Localized Tissue Injury
Frostbite is a localized injury where the skin and underlying tissues freeze, most commonly affecting extremities like the fingers, toes, ears, and nose. The initial damage occurs when the body restricts blood flow to the periphery to conserve heat for the core. This lack of warm blood allows the tissue temperature to drop below freezing, typically below 31°F (-0.55°C).
The mechanism of injury involves two phases: ice crystal formation and microvascular damage. Extracellular ice crystals form first, drawing water out of the cells and causing dehydration. Even after thawing, the damaged blood vessel linings and microthrombi lead to a lack of oxygen, causing progressive tissue death.
Frostbite progresses through stages, beginning with frostnip, which involves numbness and skin that turns pale or red without permanent damage. Superficial frostbite affects the outer skin layers, presenting with a waxy, firm feel and, upon rewarming, clear blisters. Deep frostbite involves all layers of the skin and underlying tissue, appearing white or blue-gray and feeling hard and solid to the touch.
Hypothermia: A Systemic Core Temperature Drop
Hypothermia is a systemic condition defined by a dangerous drop in the body’s core temperature to below 95°F (35°C). This condition overwhelms the body’s ability to generate heat, leading to a progressive slowdown of all physiological functions. The body attempts to compensate by shunting blood away from the skin and increasing metabolic heat production through vigorous shivering.
As the core temperature drops further, the central nervous system and cardiovascular system begin to fail. Mild hypothermia (90–95°F or 32–35°C) is characterized by intense shivering, mild confusion, and slurred speech. In moderate hypothermia (82–90°F or 28–32°C), shivering often stops, and confusion increases, sometimes leading to lethargy and clumsiness.
Severe hypothermia (below 82°F or 28°C) is life-threatening, marked by a loss of consciousness and the potential for a dangerously slow or irregular heart rhythm. At these low temperatures, brain electrical activity becomes abnormal, and the heart is susceptible to sudden cardiac arrest. The body’s regulatory mechanisms cease, requiring external heat sources for recovery.
Distinguishing Symptoms and Progression
The defining difference between the two conditions lies in their scope and impact on the body. Frostbite is an injury to specific tissues, causing visible damage like pale, waxy, or discolored skin and localized numbness. The primary threat from frostbite is the potential loss of tissue or limb function.
Hypothermia is a body-wide medical emergency that threatens life by compromising major organ function. Symptoms are systemic, focusing on altered mental status, poor coordination, and changes in consciousness. A person with hypothermia may exhibit intense shivering in the early stages, while a person with deep frostbite may not even realize the extent of the damage due to localized numbness.
In severe cases, hypothermia can lead to paradoxical undressing, where the confused person removes clothing, and a glassy stare. Severe frostbite is characterized by the affected area turning hard and black as tissue dies. Hypothermia often precedes or accompanies frostbite, making it the immediate priority for survival.
Immediate Response and Re-warming Protocols
The immediate response focuses on eliminating further heat loss and applying appropriate re-warming techniques. For frostbite, the affected area should be moved to a warm environment and gently re-warmed, ideally by soaking it in warm, not hot, water between 100°F and 105°F (37°C and 40°C). It is important never to rub the area, as this causes further mechanical damage to the fragile, frozen tissue.
For frostbite, only begin re-warming if there is no risk of the tissue refreezing before reaching medical care, as a cycle of thawing and refreezing drastically worsens the injury. The focus for hypothermia is on stabilizing the core temperature and immediately seeking emergency medical help. Wet clothing must be removed and replaced with dry layers or blankets to prevent further heat loss.
Re-warming for hypothermia should be gradual and focus on the core—the chest, neck, and head—using warm compresses or blankets. Unlike frostbite, which uses localized rapid re-warming, hypothermia requires whole-body, slow re-warming to prevent complications. If the person is alert, offering warm, non-alcoholic, non-caffeinated fluids can help raise the temperature.