Frostbite — Recognition and Field Treatment

Frostbite is the freezing of tissue — skin and the underlying structures — caused by prolonged exposure to temperatures below freezing. Ice crystals form within and around cells, causing mechanical damage and disrupting circulation. In severe cases, frostbite causes permanent tissue death, gangrene, and loss of fingers, toes, ears, or nose.

Frostbite is entirely preventable and, if caught early, entirely reversible. In its advanced stages it causes permanent injury. Field treatment decisions — particularly whether and when to rewarm — have significant consequences for outcomes.

Stages of Frostbite

Frostbite is classified by depth, similar to burns:

Stage	Tissue Involved	Appearance	Feeling	Outcome Without Treatment
Frostnip	Epidermis only	Red, white, or pale; waxy appearance	Numbness, tingling, burning	Fully reversible; no permanent damage
Superficial frostbite	Epidermis and upper dermis	White or greyish; firm to touch; blisters with clear fluid may form after rewarming	Numb; feels like "wood"	Usually reversible; blisters heal
Deep frostbite	All skin layers + underlying structures	White, grey, or blue-black; hard; blisters with blood-filled fluid	No sensation	Significant risk of tissue loss

Most commonly affected areas: Toes, fingers, ears, nose, and cheeks — areas furthest from the core and most exposed.

Recognising Frostbite

Sign	What It Indicates
Pale, white, or greyish skin	Vasoconstriction and ice crystal formation
Waxy or hard texture	Frozen tissue
Numbness in the area	Nerve conduction failure from cold
Lack of pain when the area should hurt	Loss of sensation is a warning sign
Blisters (after rewarming)	Superficial frostbite; clear blisters are better prognosis than blood-filled

Frostnip vs. frostbite: Frostnip involves redness and numbness but the skin remains soft and flexible. Frostbite involves hard, pale/white skin that does not return to normal on touching. Both require removal from the cold; only frostbite requires rewarming procedures.

The Critical Field Decision — To Rewarm or Not to Rewarm

This is the most important clinical decision in field treatment of frostbite:

The rule: Do not rewarm if there is any risk of the tissue refreezing.

Situation	Rewarm?
The person is in a warm shelter with no further cold exposure likely	Yes — begin rewarming
The person must continue walking through cold to reach safety	No — leave frozen; walking on frozen feet is painful but less damaging than rewarming then refreezing
The person is in a wilderness environment days from evacuation	Depends on conditions; if sustained warmth can be guaranteed, yes

Why this rule exists: Tissue that freezes, thaws, and then refreezes suffers catastrophically worse damage than tissue that remains frozen throughout. Ice crystals reform in already-damaged tissue, causing irreversible destruction.

If you are in the field and cannot guarantee the person will stay warm, do not rewarm. Evacuate to a warm environment first.

Field Rewarming Procedure

When you are in a warm, safe environment and refreezing will not occur:

1. Do not rub the affected area — ice crystals in tissue act as razors; rubbing causes mechanical damage.
2. Prepare a water bath — fill a container with water at 37–40°C (comfortable warm, not hot). Use a thermometer if available; test on inside of wrist.
3. Immerse the frostbitten area in the warm water bath.
4. Maintain water temperature — add warm water as it cools; the frozen tissue absorbs large amounts of heat.
5. Continue for 20–45 minutes — until the tissue is warm, soft, and colour has returned (flush pink to red; may be dark red or blotchy initially).
6. Expect significant pain during rewarming — the return of circulation in damaged tissue is very painful; analgesics should be given if available.
7. Do not use dry heat — hot water bottles, radiators, campfires; uneven temperature causes burns to numb tissue.

After Rewarming

1. Keep the area warm — do not re-expose to cold.
2. Do not walk on rewarmed frostbitten feet — the tissue is now fragile; walking causes mechanical damage.
3. Do not burst blisters — the fluid provides sterile coverage; leave intact.
4. Dress loosely with non-adherent material.
5. Evacuate to hospital — hospital treatment includes assessment for deep tissue damage, wound management, and in some cases vasodilator medications.

What Not to Do

Action	Why Not
Rub the area	Ice crystals cause mechanical cell destruction
Apply snow or cold water	Continues the freezing
Use a campfire or stove for direct heat	Burns numb tissue
Break blisters	Introduces infection; removes protective covering
Walk on rewarmed feet	Mechanical damage to fragile, damaged tissue
Rewarm if refreezing is possible	Freeze-thaw-refreeze cycle is catastrophically damaging
Give alcohol	Causes peripheral vasodilation; increases heat loss

Field Prevention

Measure	Effect
Dress in layers with moisture-wicking base layer	Keeps skin dry; reduces heat loss
Protect extremities — gloves, hat, face covering	Prevents cold exposure to most vulnerable areas
Stay dry	Wet clothing loses insulating value rapidly
Avoid tight clothing	Constriction reduces blood flow
Eat and drink adequately	Dehydration and low blood sugar reduce cold tolerance
Recognise early signs	Numbness, tingling, pale skin — respond before frostbite develops
Buddy check	In extreme cold, check each other's faces regularly

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Quick Reference

Stage	Signs	Field Action
Frostnip	Red, numb, soft skin	Warm gently; protect from further cold; no other treatment
Superficial frostbite	Pale/white, slightly firm	Rewarm in warm water bath only if no refreeze risk
Deep frostbite	Hard, white/grey/black, no sensation	Evacuate; do not rewarm in field if refreeze possible
Do not rewarm if	Still in cold; must walk far; refreeze possible	Leave frozen; evacuate
Rewarm temperature	37–40°C water bath	Not dry heat; not very hot water
After rewarming	No walking; no burst blisters; hospital