Frostbite and cold injury

• Frostbite is a freezing injury of skin and deeper tissues at temperatures below 0 °C; frostnip, just above it, is a reversible non-freezing cold injury in which no ice forms within the tissues. ^[1][2]
• Severity is judged after rewarming: superficial (first/second degree, minimal tissue loss) versus deep (third/fourth degree, tissue loss likely), with the Cauchy grade 1 to 4 predicting the level of amputation.
• The single most damaging field event is thawing tissue that then refreezes: if refreezing is possible, keep the part frozen until it can be kept thawed.
• Otherwise rewarm in warm water at 37 to 39 °C (or 40 to 42 °C when following military guidance) for about 15 to 30 minutes, until the tissue is soft, pliable and red or purple. ^[5]
• Ibuprofen at 12 mg per kg per day divided twice daily (up to 2400 mg per day in four doses) is given routinely; thrombolysis with tPA is for deep, thawed, limb-threatening frostbite within 12 to 24 hours; iloprost is given for grades 2 to 4 up to 72 hours. ^[4][5]
• Non-freezing injuries (frostnip, chilblains, trench foot) occur at or above freezing with wet cold; chilblains is usually self-limited, while trench foot can leave months of neuropathic pain. ^[8]
• Frostbite and hypothermia often occur together: correct moderate or severe hypothermia before or alongside local rewarming, and always check the whole patient for cold exposure.

By the end of this page you should be able to:

1. Tell frostnip, superficial frostbite, deep frostbite and non-freezing cold injuries apart by mechanism and appearance.
2. Stage a frostbite injury after rewarming and use the Cauchy grade to estimate amputation risk.
3. Plan field rewarming, including when not to thaw, the water temperature, duration and analgesia.
4. Choose between thrombolysis and iloprost in hospital, with their time limits, routes, doses and monitoring.
5. Recognise and manage chilblains and trench foot, including the limits of nifedipine evidence.
6. Screen for concurrent hypothermia or hypoxia and apply prevention and low-resource measures.

Frostbite is part of a spectrum of cold-weather injury. Two ideas separate it from its neighbours: the temperature has to be below freezing for ice to form, and the damage happens in two phases, an initial freeze and a later thaw-related injury. This page also covers the non-freezing injuries that look similar but need different treatment.

Frostbite is classified in two ways that answer different questions, and both are used in practice.

• The four-degree (burn-like) scheme describes depth: first degree gives numbness, redness, swelling and peeling without tissue loss; second degree gives clear or milky blisters on a red, swollen base; third degree gives haemorrhagic blisters because the injury has reached the deeper dermal vessels; fourth degree is full-thickness injury into muscle, tendon and bone, with mummification and a high amputation risk. ^{[1] [1]}
• The two-tier field scheme favoured by the Wilderness Medical Society (WMS) is what you can actually use at the bedside or on the mountain: superficial (first or second degree, little or no tissue loss expected) versus deep (third or fourth degree, tissue loss expected). ^{[2] [3]}
• The Cauchy 1 to 4 grading used in hospital is based on how far discoloration extends after rewarming and, with a day-2 bone scan, predicts the eventual amputation level: grade 1 rarely needs amputation, while grade 4 predicts amputation of the extremity with possible systemic involvement or sepsis. ^[1]

People at highest risk are those with poor perfusion or poor self-care: infants and older adults, people experiencing homelessness, outdoor workers and mountaineers, and anyone with peripheral vascular disease, diabetes, Raynaud phenomenon, hypothyroidism, malnutrition, dehydration, altered mental status, tobacco, alcohol or drug use, or tight footwear. ^{[1] [1]}

Frostbite injury occurs when tissue heat loss exceeds the ability of local perfusion to prevent freezing: blood flow delivers heat. Prevention therefore means both ensuring perfusion (adequate core temperature, hydration, nutrition, unrestricted circulation) and minimising heat loss (covering skin, removing moisture, limiting exposure). ^{[2] [3]}

Specifically, the risk rises with:

• environmental: temperatures below 0 °C, with significant risk below minus 15 °C even with light wind; high wind, high altitude above 4000 m, wetness, and subzero immersion. ^{[3] [4] [2]}
• personal: older age, homelessness, alcohol or drug intoxication, altered consciousness, malnutrition, dehydration, impaired circulation, Raynaud phenomenon, tight or wet clothing and footwear. ^{[1] [2]}

A frostbite injury moves through four overlapping phases, and understanding them explains most of the management:

1. Prefreeze. There is intense vasoconstriction and tissue cooling. Nerves become hypoxic, producing numbness and paraesthesia; ice has not yet formed and damage is still reversible. ^{[4] [1]}
2. Freeze-thaw. Extracellular ice crystals form, pulling water out of cells by osmosis; with prolonged cooling ice also forms inside cells, rupturing membranes. Rewarming then triggers a reperfusion injury with reactive oxygen species and an inflammatory cascade. ^[1]
3. Vascular stasis. Endothelial swelling, leakage, haemoconcentration, microvascular thrombosis and stasis coagulation shut down perfusion; this is the phase thrombolysis and vasodilators aim at. ^{[4] [1]}
4. Late ischaemia. Progressive ischaemia and infarction lead to necrosis and, if unchecked, to gangrene and possible autoamputation. ^[1]

Repeated freeze-thaw cycles multiply the damage, which is why a frozen part that may refreeze should not be thawed until the thaw can be sustained. ^{[2] [1]}

The history is dominated by the conditions of exposure: ambient temperature, wind, moisture, altitude, duration, whether the extremity was wet or constricted, and any attempts at thawing. Patients may report heaviness or numbness before the pain; with deep injury the part can be pale, cold, hard and without sensation. ^[1]

Examination after thawing shows the degree-based findings. Edema typically develops after thawing and blisters form within 24 to 48 hours; with deep injury there is blue-grey discoloration, non-blanching cyanosis, haemorrhagic or clear blisters, and later eschar formation. Demarcation between viable and dead tissue can take 1 to 3 months or more. ^{[1] [1]}

Any frostbite patient should also be assessed for concurrent hypothermia, trauma, hypoxia and exhaustion.

The conditions most likely to be confused with frostbite, and the features that separate them:

The diagnosis is clinical. In equipped centres, imaging can speed the decision about tissue viability and surgery:

• Technetium-99m bone scintigraphy, SPECT/CT and magnetic resonance angiography can show which tissue is still perfused and where the line of demarcation will lie, supporting earlier surgery. ^{[1] [5]}
• Conventional angiography is used before and during intra-arterial thrombolysis to look for impaired perfusion. ^[5]
• Blood tests are not diagnostic, but fever or a raised white cell count with wet gangrene changes management; electrolytes may be disturbed with rhabdomyolysis after rewarming in severe cases. ^{[1] [5]}

Use the four-degree description for what you see, the two-tier system for triage, and the Cauchy grade to predict amputation and to select thrombolysis or iloprost:

1. Treat the person, not only the hand or foot. Look for and correct hypothermia, serious trauma, hypoxia and exhaustion first; moderate or severe hypothermia should be treated before local frostbite management. ^{[1] [3]}
2. Remove wet or constricting clothing, jewellery and footwear. ^[2]
3. Protect the frozen part from further damage and do not rub, massage or apply snow or ice. ^{[2] [5]}

The crucial field decision is whether to thaw at all:

• If refreezing is possible, do not thaw. Keeping frozen tissue frozen is safer than a thaw followed by a refreeze, which is the most damaging sequence. Protect, pad, splint, keep dry, and evacuate. ^{[2] [5]}
• If the thaw can be sustained (definitive care is more than 2 hours away and the part can be kept warm), perform rapid rewarming in a warm water bath. ^[2]
  • Water at 37 to 39 °C (98.6 to 102.2 °F) is recommended by WMS; some field guidance uses 40 to 42 °C (104 to 107.6 °F). Either way, use a thermometer if possible, and never use an oven, stove, heater or very hot water, because anaesthetic tissue burns. ^{[2] [4] [5]}
  • Immerse with water circulating; rewarming is complete in roughly 15 to 30 minutes when the skin becomes soft, pliable, flushed, red or purple. ^{[2] [5]}
  • If a thermometer is unavailable, a caregiver's hand should tolerate the water for at least 30 seconds. ^{[2] [5]}
  • Let spontaneous or passive thawing occur if rapid sustainable rewarming is impossible. ^[2]
• Analgesia during thawing is important; use a multimodal approach (NSAIDs, acetaminophen, and opioids if needed), plus anti-inflammatories for prostaglandin blockade. ^{[2] [5]}
• Medication in the field: ibuprofen at 12 mg per kg per day divided twice daily up to a maximum of 2400 mg per day in four doses, unless contraindicated. ^{[3] [4] [1]}
• Clear, tense blisters may be drained by needle aspiration in the field; haemorrhagic blisters are left intact. Apply topical aloe vera every 6 hours, with dry, bulky dressings; elevate the part and give hydration (warm intravenous fluids if needed, in small boluses). ^{[2] [1]}
• Oxygen at flow sufficient to relieve hypoxia (oxygen saturation below 88 percent) or at altitudes above 4000 m. ^[2]

• Treat hypothermia, trauma, hypoxia and re-warm first; systemic hydration and pain control. ^{[1] [3]}
• Thrombolysis (tPA) is for thawed, deep, limb-threatening frostbite with evidence of vascular compromise (Cauchy grades 3 or 4):
  • only within about 24 hours of injury or thawing (some guidance prefers 12 hours); each hour of delay reduces digit salvage. ^{[3] [4] [5]}
  • intravenous: 0.15 mg per kg bolus then 0.15 mg per kg per hour (up to 100 mg over 4 to 6 hours), followed by therapeutic heparin for 3 to 5 days. ^{[3] [5] [4]}
  • intra-arterial: 2 to 4 mg bolus then 0.5 to 1 mg per hour (up to 24 to 48 hours) via brachial or femoral catheter, with concurrent heparin at 500 units per hour; angiography assesses perfusion. ^{[3] [5]}
  • contraindicated after about 48 hours, with a freeze-thaw-refreeze course, or with bleeding risk, concurrent trauma, haemorrhage, bleeding disorders or recent surgery. ^[5]
• Iloprost, a prostacyclin analogue approved by the FDA in February 2024 for severe frostbite, is given for deep frostbite to the distal interphalangeal joint or proximal (Cauchy grades 2 to 4) up to 72 hours after rewarming, ideally as soon as possible. It can be given in centres without angiography and avoids the bleeding risk of tPA. ^{[1] [3] [4]}
  • Earlier WMS guidance suggested 0.5 nanograms per kg per minute rising to a maximum of 2.0 nanograms per kg per minute for 6 hours daily; the 2024 guideline does not set a dose. ^[4]
• Supportive measures: selective drainage of clear blisters, leaving haemorrhagic blisters, topical aloe vera every 6 hours, hydrotherapy 1 to 2 times daily after edema settles, dry loose dressings with digits separated, hyperbaric oxygen where available (evidence limited), physiotherapy and occupational therapy. ^{[1] [4] [5]}
• Surgery (debridement, grafting, flap, amputation) is delayed until tissue is fully demarcated, usually 1 to 3 months, except for compartment syndrome, wet gangrene or sepsis, which need urgent action. ^{[1] [5]}
• Low-molecular-weight dextran can be used when thrombolysis or iloprost is unavailable. ^{[4] [3]}
• Antibiotic prophylaxis is not needed; treat antibiotics only if infection is present. ^[1]
• Tetanus prophylaxis according to immunisation status. ^{[1] [3]}

• Infection, cellulitis, osteomyelitis and sepsis from wet gangrene. ^{[1] [5]}
• Compartment syndrome after rewarming requiring fasciotomy. ^[1]
• Late: residual neuropathic pain, cold sensitivity for up to a year, hyperhidrosis, clawing, joint stiffness, contractures, osteoarthritis-like changes in severe cases, and possible (rare) growth-plate damage in children. ^{[1] [1]}
• Recurrent freeze-thaw courses, prolonged time to treatment and harsher conditions predict deeper injury and amputation. ^{[1] [1]}

Superficial frostbite often heals over days to weeks. Deep injury needs 1 to 3 months or longer for full demarcation. Cauchy grade 4 carries a very high predicted amputation risk, while outcomes with tPA or iloprost in published series are markedly better; the evidence remains single-study or observational. Most survivors have some residual sensory or functional deficit, and cold sensitivity can persist for up to a year. ^{[1] [5] [1]}

• Avoid conditions below minus 15 °C where possible; minimise duration of exposure and protect all skin and scalp. ^{[2] [3]}
• Maintain core temperature, hydration and nutrition. ^[2]
• Cover skin, avoid wet extremities, constrictive footwear and constricting clothing; change socks frequently. ^[2]
• Exercise can help perfusion, but avoid exhaustion. ^[2]
• Chemical and electrical warmers may be used, but never directly on skin and never if still too hot after activation. ^[2]
• Emollients such as creams and lotions do not protect against frostbite and may increase risk. ^[2]
• Screen anyone with numb or painful extremities early, especially people experiencing homelessness and outdoor workers. ^{[2] [6]}

• Children. Frostbite is less common than in adults but should prompt safeguarding and prevention advice. Growth-plate damage has been described with deep injury. ^{[1] [1]}
• Older adults and people with vascular disease, diabetes or Raynaud phenomenon. Higher risk of deeper injury and amputation; may present late. ^{[1] [1]}
• Pregnancy. Manage as for other cold injury; no pregnancy-specific frostbite dose in current guidelines. ^[3]
• Concurrent hypothermia. Treat first when moderate or severe, using warmed intravenous fluids and other whole-body methods; mild hypothermia can be corrected alongside local rewarming. Core temperature below 35 °C is hypothermia. ^[1]

• Simplest effective treatment is a warm water bath at 37 to 39 °C (or 40 to 42 °C if following military protocols), a thermometer or caregiver-hand test, dry dressings, aloe vera gel where available and oral ibuprofen. ^{[2] [5]}
• If thrombolysis, iloprost, imaging or surgical care are unavailable, evacuation to a centre with frostbite experience is the priority.
• Address alcohol use, footwear and shelter, which reduce preventable re-injury more than any drug.
• Chilblains can be treated with warmth and dryness alone; nifedipine is cheap but its benefit is doubtful (see below).

Frostbite is a local freezing injury; hypothermia and hyperthermia are general temperature disorders. Frostbite and hypothermia often occur together, and a person can be hypothermic while a single extremity is frozen. In contrast, hyperthermia is failure of heat dissipation with a normal set point, which does not produce frostbite and is managed by cooling, not warming. Check the whole patient: core temperature below 35 °C defines hypothermia and takes priority in management; the details of heat stroke are in the separate hypothermia and hyperthermia topic.

Trench foot, also called immersion foot or non-freezing cold injury, occurs with prolonged exposure to wet cold at or above freezing (0 to 15 °C), often with poor hygiene or tight footwear. Ice does not form, but nerves and microvessels are injured. ^{[6] [1] [8]}

• Early: numb, cold, pale or erythematous, swollen, clammy foot; may have gait disturbance from loss of proprioception. ^[6]
• On rewarming: mottled or cyanotic foot that becomes hyperaemic with bounding pulses, often very painful with hyperalgesia that can persist for 6 to 10 weeks. Autonomic dysfunction (sweating, vasomotor change) and chronic sensory loss or muscle atrophy can follow. ^[6]
• First, treat hypothermia and frostbite if present; then passive rewarming at room temperature, elevation, and sterile dressings. ^[6]
• Prevention centres on dry feet and socks, well-fitting boots and rotation out of cold wet conditions. ^[6]
• Chronic neuropathic pain is difficult; amitriptyline then gabapentin may help; some centres report early iloprost benefit in selected patients (small studies). ^{[6] [8]}

Chilblains are recurring itchy, sometimes painful, purple-blue swollen areas on fingers, toes or the pretibial area after repeated damp cold exposure, most often in women, and may associate with Raynaud phenomenon or autoimmune disease. It is usually self-limited over 1 to 3 weeks but may recur each winter. ^{[6] [7]}

• First-line treatment is conservative: keep warm and dry, avoid nicotine, avoid re-exposure. ^[6]
• Drug evidence is weak: topical glucocorticoids and nifedipine (often cited historically at 60 mg per day, with a trial regimen of 30 mg controlled release daily for 2 weeks then 30 mg twice daily for 4 weeks) are commonly used but a randomised placebo-controlled trial of nifedipine 60 mg per day in 32 patients found no advantage over placebo and more oedema. Pentoxifylline or tadalafil may also be tried. ^{[7] [6]}
• Because chilblains can be secondary to systemic disease, resistant or chronic cases warrant basic workup (blood count, autoimmune screen, cryoglobulins, antiphospholipid antibodies and serum protein electrophoresis). ^[7]

• Frostbite is a freezing injury below 0 °C with a freeze and a separate thaw-related reperfusion injury; superficial (first/second degree) and deep (third/fourth degree) predict outcome.
• Frostnip is reversible, with no tissue ice and no permanent loss; it is the warning sign to rewarm before frostbite develops.
• The most dangerous field error is thawing tissue that then refreezes; if refreezing is likely, keep it frozen.
• Rapid rewarming at 37 to 39 °C (or 40 to 42 °C in military practice) for about 15 to 30 minutes, until soft, pliable and flushed, is the core treatment. ^[2]
• Ibuprofen 12 mg per kg per day divided twice daily (maximum 2400 mg per day in four doses) should be started early; opioids help reperfusion pain.
• Thrombolysis with tPA is life- and limb-saving for deep, thawed, vascularly compromised injury within about 12 to 24 hours; heparin as an adjunct, never as monotherapy.
• Iloprost covers Cauchy grades 2 to 4 up to 72 hours, including centres without angiography, and was FDA-approved for severe frostbite in February 2024. ^[2]
• Clear blisters may be drained; haemorrhagic blisters are left alone; aloe vera topically every 6 hours helps; surgery is delayed 1 to 3 months for demarcation.
• Hypothermia (core below 35 °C) frequently coexists and takes priority when moderate or severe; hyperthermia is a different disorder treated by cooling.
• Trench foot follows wet cold above freezing and may leave months of neuropathic pain; chilblains is usually self-limited, and routine nifedipine is not supported by the best trial.
• Prevention beats treatment: avoid dangerous cold, keep dry and perfused, and remember emollients do not protect against frostbite.

Cold injury is cross-checked against the separate text on hypothermia and hyperthermia. Other closely related topics include burns and inhalation injury, accidental and deliberate poisoning, trauma resuscitation, local and regional anaesthesia, peripheral neuropathies and Raynaud phenomenon. If your system lists them as verified topics, open them in this order: hypothermia and hyperthermia first, then trauma assessment, then wound and burn management. (No automatic links are provided for these so that the page stays readable; the published site will wire them where available.)