Frostbite

How the tissue is damaged

Warm blood keeps the outer parts of the body functional. In the cold, the body narrows blood vessels in the skin to retain heat in the core. Fingers and toes then receive less warmth. Wind accelerates heat loss, wetness reduces insulation, and tight footwear or straps further restrict circulation. Direct contact with cold metal or deeply chilled fuel can draw heat from the skin particularly quickly.

Freezing produces ice crystals that damage cells directly or draw water out of them. After thawing, inflammation, swelling and clots in small vessels can further impair the blood supply. The injury can therefore progress even after the body part becomes warm again. Refreezing after thawing intensifies these processes and can destroy substantially more tissue.

Numbness is a warning

Tingling, burning or cold pain can give way to numbness. Pain disappearing at this point does not indicate recovery: cooled nerves become less able to signal continued cooling. Unusual clumsiness, pale or waxy-looking skin and a numb, hard body part call for immediate protection. There is no reliable waiting period between numbness and frostbite.

A pale, numb patch of skin can initially result from severe vessel constriction without the tissue itself being frozen. This early condition is called frostnip; sensation and normal colour return promptly with protection and warming. Pallor alone, however, cannot establish that an injury is harmless frostnip. While tissue remains frozen, the true depth of injury is difficult to assess. Swelling and blisters often become more evident after thawing; blood-filled blisters suggest deeper injury. Different degrees of injury can also coexist in the same hand or foot.

Protecting the ability to act

As soon as sensation begins to decline, use the next genuinely reachable shelter from the wind and cover exposed skin. Wrap available clothing material around the hands or hold them against the warm trunk beneath clothing; cold fingers that are still soft can be warmed in your own armpits without rubbing. Loosen restrictive glove straps, lacing or equipment without losing protection from the cold. Remove rings and other removable constricting items early, while this can be done without force. Swelling can prevent removal later.

Feet need both insulation and enough room for circulation. Adding a sock to an already tight boot can reduce protection. Replace wet socks or gloves with dry ones when replacements are available and the change can be made under shelter. Without replacements, first limit wind exposure and further wetting; undressing in the open does not provide dry insulation. Do not blow into gloves: moisture from the breath wets the fabric and can freeze in it. Use available gloves or a suitable fabric barrier when handling cold metal rather than gripping it with bare skin.

Mittens keep fingers warmer together but make fine movements harder. If they must be opened for a fastener or device, prepare the task and cover the hand again afterwards. Before another stretch of exposed ground, check whether sensation, grip and secure footing remain. A route along the sheltered side of terrain can reduce cold exposure; a longer detour consumes additional time and energy. Hard exercise cannot replace protection: sweat wets insulation and exhaustion reduces heat production. Loading already injured limbs causes further damage.

Deciding whether to thaw

When frostbite is suspected, also look for hypothermia. Confusion, marked drowsiness or unsteady walking after cold exposure indicate a threat to the whole body. Protection from wind and precipitation, insulation from the ground and preserving trunk warmth then take priority over a local water bath. Food and drink are appropriate only with clear consciousness and effective swallowing.

Deliberate thawing requires the injured part to remain warm and protected afterwards. This includes the onward route and any possible pickup: brief warming followed by renewed cold exposure can turn frostbite into a more severe thaw-refreeze injury. A hide site sheltered from the wind can reduce heat loss while still failing to provide enough warmth for that requirement. Where refreezing is a real risk, initially protect the part from wind and mechanical injury and postpone deliberate thawing. Do not cool it with snow or intentionally keep it frozen. Once sustained warmth is possible, allow it to thaw slowly through the environment and body heat as well.

Rewarming with the means actually available

If a sheltered warm place, a suitable container and enough warmed water are available, frozen tissue can be thawed in a controlled water bath. Maintain the water at 37–39 °C; the body part must not touch a hot container wall or heated base. Continue monitoring the temperature and cautiously replace cooled water. Without a thermometer, fully immerse an uninjured hand with normal sensation for at least 30 seconds: the water must remain very warm but comfortably tolerable throughout this check. Check the temperature again after reheating or replacing water. Numb or injured fingers cannot reliably detect a burn. If this check is also impossible, forgo an improvised hot bath.

The time needed for thawing varies. It is complete when the tissue has become soft and pliable and has taken on a red to purple colour; substantial pain can occur during rewarming. Afterwards, allow it to air-dry or gently blot it dry. Without the means for a safely controlled bath, the alternatives are a persistently warmer sheltered place and your own body heat, such as placing fingers in the armpits. This warming also requires the thawed tissue to remain protected from refreezing afterwards. Do not rub, massage or apply snow. Open flames, stoves, vehicle exhaust, hot stones and directly applied heat packs can burn tissue that lacks sensation.

The injury changes the onward route

Keep thawed tissue dry, loosely covered and protected from pressure and impacts. If clean, dry dressing material is available, apply soft padding and separate fingers or toes; the covering must leave room for swelling. Do not puncture blisters or tear away skin yourself. A foot can swell after thawing until a removed boot no longer fits. Before a water bath, therefore, establish how the foot can subsequently be protected and how you can move, rather than forcing the boot back over an injured foot later.

Avoid loading an injured foot wherever possible; this also applies to tissue that is still frozen. Walking on an entirely affected foot risks greater damage than walking with a limited toe injury. If an immediate threat nevertheless forces movement, minimise the necessary distance to genuinely reachable protection, pad the foot without constricting it where possible, and limit impacts or forceful rolling through each step. After thawing, skin and tissue are particularly vulnerable. A route plan that continues to require normal speed, long distances or climbing no longer matches your physical capacity.

Persistent numbness, hard tissue, blisters, pronounced discolouration or loss of hand and foot function call for medical assessment as soon as it becomes genuinely reachable. Protection can limit further damage; it cannot restore an already destroyed blood supply. If usable communications, a connection and reachable forces are available, report your position, affected body parts and remaining mobility. During pickup, the injuries still need protection from cold, pressure and airflow.

Frostbite and Freezing Cold Injury

Frostbite is called Erfrierung in German. British military documents use Freezing Cold Injury, or FCI, as an umbrella term that also includes frostnip. The label FCI alone therefore does not establish whether tissue has actually frozen or how deep the damage extends. Non-Freezing Cold Injury refers instead to local damage from prolonged cold and wet exposure without tissue freezing. The practical distinction is whether there is early cooling to reverse, a frozen injury to protect, or already thawed tissue to preserve from renewed cold and loading.