Frostbite: What Happens to the Tissue and What Not to Do
Frostbite is tissue freezing, and the most common first aid for it makes it worse. How to tell frostnip from deep frostbite, and how to warm it safely.
Jarrett Chisholm, ACP · October 28, 2026
Where this is taught: Wilderness First Aid, Wilderness First Responder and First Responder.
Almost everyone who grew up in Alberta has been told to rub a frozen ear or cheek, or to hold frozen hands close to the fire. Both are among the worst things you can do to frostbitten tissue. The instinct is to get the heat back in fast and the feeling back with it. The tissue needs something much gentler than that.
Image needed · hero
frozen-hands-warming-in-basin-of-water.jpg
Indoor, warm kitchen or trailer lighting. A pair of pale, slightly waxy-looking hands rest in a plastic basin of water on a table. A first aider's hand holds a simple thermometer in the water. Towels and a folded blanket nearby. Make-up for pallor is fine; no blisters or black tissue.
Alt text ready: “A person's pale hands resting in a basin of warm water on a table while a first aider checks the water temperature with a thermometer.”
Frostbite is exactly what it sounds like: skin and the tissue underneath it freezing. It most often affects the parts of the body furthest from the core and most exposed to wind: fingers, toes, ears, the nose and the cheeks. It can happen in minutes when skin is exposed in a hard wind, and it is common in people who are working with bare hands, wearing wet gloves or tight boots, or not moving much in the cold.
This post explains what is happening inside frozen tissue, because once you understand that, the rules for treating it stop feeling arbitrary. the winter injuries worth knowing before the cold arrives.
What is actually happening
When skin gets very cold, the body narrows the blood vessels feeding it to protect the core. Less warm blood reaches the fingers and toes, so they cool faster still. If the tissue gets cold enough, ice crystals form in and between the cells. The crystals damage the cells directly, and the small blood vessels in the area are injured too.
The second part of the damage happens when the tissue thaws. The injured blood vessels can leak and clot, cutting off blood to tissue that survived the freezing itself. This is why how the tissue is rewarmed matters so much, and why freezing again after thawing is so destructive: every cycle adds another round of injury.
Frozen tissue is also numb. The person usually cannot feel how badly it is damaged, cannot feel heat properly, and cannot tell if something is burning them. That is where the damage from a fire, a heater or hot water comes from.
Frostnip, superficial and deep
Cold injury to the skin is a range, not a single thing. Where a particular injury sits on that range decides whether it can be managed at home or needs a hospital.
| Degree | What you see and feel | What it usually means |
|---|---|---|
| Frostnip | Red or pale skin, stinging or tingling, soft to the touch, feeling returns quickly with warming | Surface only. Warm it and protect it. No lasting damage expected. |
| Superficial frostbite | Hardened, pale or waxy skin that looks paler than the skin around it, stinging then numbness, tissue underneath still gives when pressed | Skin layers are frozen. Warm carefully and have it assessed. Blisters may form after warming. |
| Deep frostbite | Skin and the tissue below are hard and solid, white, blue, grey or mottled, with complete loss of feeling | Deeper tissue is frozen. Needs hospital care. Some treatments work best early, so do not wait to see how it looks tomorrow. |
Image needed · diagram
frostbite-depth-frostnip-superficial-deep.svg
Three side-by-side cross-sections of a fingertip or skin block, each labelled. Frostnip: a thin pale band at the very surface. Superficial: ice-crystal pattern through the skin layers only. Deep: ice through skin and into the tissue below, with a small note that the tissue feels hard. Cool blue-grey for frozen areas, Delta gold labels, charcoal line work.
Alt text ready: “Cross-section diagram of skin showing three depths of cold injury: frostnip at the surface, superficial frostbite through the skin layers, and deep frostbite reaching the tissue below.”
You will not always be able to tell superficial from deep frostbite in the field, and the full extent is often not clear for days. If the skin is hard, pale and numb and stays that way, treat it as serious.
What not to do
Most frostbite first aid is about avoiding a handful of well-meant mistakes. Each one makes the damage worse for the reasons above.
The mistakes to avoid:
- Do not rub or massage frozen skin, and do not rub it with snow. The ice crystals in the tissue grind against the cells.
- Do not warm it with dry heat: a fire, a heater, a car vent, a heating pad. Numb skin burns without the person feeling it.
- Do not thaw it if there is a real chance it will freeze again before you reach shelter.
- Do not break blisters that form after warming.
- Do not let the person walk on feet once they have thawed, if you can avoid it.
- Do not give alcohol to warm them up.
The single biggest decision in the field is whether to thaw at all. If the person still has to walk out, drive a long way, or go back out into the cold, it is often better to keep the frozen part frozen, protected and padded, until you reach somewhere it can be warmed and kept warm. Thawing and then refreezing does more damage than staying frozen a little longer. the wilderness responder course, for managing cold injury far from a hospital.
How to warm it safely
Once you are somewhere warm and the area will stay warm, remove anything tight: rings, watches, boots, wet gloves. Then warm the frozen part in warm water, not hot. MyHealth Alberta advises warm water for 15 to 30 minutes and never above 42 °C. The Wilderness Medical Society's 2024 frostbite guideline recommends water kept between 37 and 39 °C, which is close to body temperature and should feel comfortably warm, not hot, to an unaffected hand. Keep adding warm water as it cools, and keep going until the skin is soft and pliable and colour starts to return.
Rewarming frostbite hurts, often a lot, as feeling comes back. That is expected. If you have no warm water, warm the area against someone else's skin: frozen fingers in an armpit or on a belly, frozen feet against a warm stomach. It is slower but it is gentle.
Afterwards, let the skin air dry rather than rubbing it with a towel, and cover it loosely with dry dressings. Put gauze or clean cloth between affected fingers or toes so they do not stick together. Raise the area if you can, keep the person warm and give them fluids to drink if they are alert.
If there is any sign of hypothermia as well, such as confusion, slurred speech, or shivering that has stopped, deal with that first. The body's core temperature matters more than a finger. Tomorrow's post covers that in detail.
When it needs a hospital
Frostnip that warms quickly and returns fully to normal colour and feeling can usually be watched at home. Anything that stays hard, pale, grey, blue or numb after warming, anything that blisters, and any frostbite on the face, hands or feet in a child or older adult needs medical assessment. Deep frostbite is a hospital injury, and some of the treatments that can save tissue are time sensitive. If in doubt, go in. the First Responder course taken by many outdoor and industrial crews.
Quick answers
- Should you rub frostbite?
- No. Rubbing or massaging frozen tissue, including rubbing it with snow, damages it further. Warm it gently in warm water or against someone's skin instead, and let it air dry afterwards.
- What temperature water should you use for frostbite?
- Warm, not hot. MyHealth Alberta advises never above 42 °C. The Wilderness Medical Society recommends 37 to 39 °C, close to body temperature, kept warm until the skin is soft and colour returns, usually 15 to 30 minutes.
- Should you thaw frostbite right away?
- Only if it will stay warm afterwards. Thawing and then refreezing causes more damage than leaving it frozen a little longer. If the person still has to go back out into the cold, protect and pad the area and warm it once you reach shelter.
- When does frostbite need a doctor?
- When the skin stays hard, pale, grey, blue or numb after warming, when blisters form, or when the face, hands or feet of a child or older adult are affected. Deep frostbite needs hospital care, and some treatments work best early.
Sources
- Alberta Health Services (MyHealth.Alberta.ca): Do not rub or massage frozen skin; do not rewarm if refreezing is possible; warm in warm (not hot) water for 15 to 30 minutes, never above 42 °C; pad and wrap frozen fingers or toes. (checked 2026-09-23)
- International Journal of Environmental Research and Public Health (summary of Wilderness Medical Society guidelines): Summary of the WMS 2024 frostbite guideline: rewarm in water at 37 to 39 °C, air dry without rubbing, avoid refreezing, do not use dry heat, immobilise the affected limb, and treat moderate or severe hypothermia before frostbite. (checked 2026-09-23)
- Canadian Red Cross: First Aid and CPR manual: signs of superficial and deep frostbite; thaw only if it will not freeze again, protect with loose dry dressings with gauze between digits, leave blisters intact, elevate and rehydrate. (checked 2026-09-23)