Frostbite is freezing of the skin and underlying tissue caused by exposure to extreme cold. Ice crystals literally form inside and between your cells, damaging them from the inside out. It most commonly affects fingers, toes, ears, nose, and cheeks, and can range from a mild, fully reversible injury to one that results in permanent tissue loss and amputation.
How Frostbite Damages Your Tissue
When your body gets cold enough, it redirects blood flow away from your extremities to protect your core organs. Blood in the smaller vessels thickens and slows, and the tissue at the edges of your body loses its heat source. Once the tissue temperature drops below freezing, ice crystals begin forming between and inside cells.
Those ice crystals do two things. First, they physically puncture and tear cell membranes as they grow. Second, they pull water out of your cells through osmosis, dehydrating them and disrupting their internal chemistry. The longer the exposure continues, the larger the crystals get and the more cells are destroyed. Interestingly, how fast the freezing happens matters: rapid freezing (from touching a highly conductive metal surface in extreme cold, for example) tends to form more ice inside the cells, while slower freezing forms ice primarily in the spaces between cells. Both are damaging, but through slightly different mechanisms.
Frostnip vs. Frostbite
Frostnip is the precursor to frostbite. Your skin gets red, cold, and prickly, but no ice crystals have formed in the tissue yet. It’s uncomfortable but fully reversible with simple rewarming. Once actual ice crystals form in the tissue, you’ve crossed from frostnip into frostbite, and permanent damage becomes possible.
The Four Degrees of Severity
Frostbite is graded on a scale similar to burns, from first degree to fourth degree. The trouble is that it’s often impossible to tell how deep the damage goes until days after the injury, once the tissue has fully rewarmed and the body’s inflammatory response has played out.
- First degree: Numbness, pale or white skin in the center with redness and swelling around it. The outer layer of skin may peel in the days that follow. Sensation often feels abnormal, with tingling or burning.
- Second degree: Blisters filled with clear or milky fluid appear on the skin within a day or two, surrounded by redness and swelling. The skin beneath the blisters is still intact.
- Third degree: The full thickness of the skin is destroyed. Blisters appear dark or blood-filled rather than clear. The tissue underneath feels hard or waxy.
- Fourth degree: Damage extends past the skin into muscle, tendon, or bone. The affected part eventually turns black as the tissue dies. A hard, dark shell may form and eventually fall away. This degree frequently results in partial or complete loss of the affected body part.
How Quickly It Can Happen
Temperature alone doesn’t tell the full story. Wind dramatically accelerates heat loss from exposed skin. At 0°F with no wind, exposed skin might take over 30 minutes to freeze. Add a 15 mph wind and the wind chill drops to around -19°F, and freezing can happen in just a few minutes. At -20°F with a 45 mph wind, the National Oceanic and Atmospheric Administration warns frostbite can set in within 5 minutes.
Wet skin, wet clothing, and direct contact with cold metal or frozen surfaces all speed things up considerably. Altitude matters too: the combination of cold, wind, and lower oxygen levels at high elevations makes mountaineers especially vulnerable.
Who Is Most at Risk
Anyone can get frostbite in the right conditions, but certain factors make it more likely or more severe. The biggest behavioral risks are straightforward: inadequate clothing, lack of access to shelter, and alcohol or drug use (which impair judgment and dilate blood vessels near the skin, accelerating heat loss).
Several medical conditions worsen frostbite outcomes because they already compromise blood flow to the extremities. Diabetes, peripheral vascular disease, and Raynaud’s disease all reduce circulation to the fingers and toes under normal conditions. When cold stress is added, these tissues lose their blood supply faster and freeze sooner. Dehydration thickens the blood, making it harder to perfuse small vessels. Smoking has a similar effect by chronically narrowing blood vessels. Malnutrition and hypothyroidism also appear on the list of conditions that increase vulnerability.
What to Do if It Happens
The standard first-aid approach is rapid rewarming in warm water between 98°F and 108°F (38–42°C) for 15 to 30 minutes. The water should feel warm but not hot to an uninjured hand. This is the single most important treatment step, and getting it right significantly affects outcomes.
There are a few critical things to avoid. Do not rub or massage the frozen tissue. Friction doesn’t help and can grind ice crystals through cell membranes, making the damage worse. Do not use dry heat like a heating pad, campfire, or car heater, because frostbitten skin has no sensation and burns easily without you feeling it. And critically, do not rewarm the tissue if there’s any chance it will refreeze before you reach shelter or medical care. Refreezing after thawing causes far more damage than leaving the tissue frozen for a longer period.
Rewarming is intensely painful. As blood flow returns and damaged nerves reactivate, most people experience severe burning or throbbing. This is actually a sign that the process is working, but it’s important to be prepared for it.
Signs That Need Immediate Medical Attention
First-degree frostbite can often be managed at home with gentle rewarming. Anything beyond that needs professional evaluation. Blisters of any kind, skin that stays white or gray after rewarming, skin that feels hard or waxy to the touch, or blood-filled blisters all indicate deeper damage that requires medical treatment. If your skin turns black or significantly darker than your natural skin tone, that signals tissue death and you should get to an emergency room.
Long-Term Effects
Even mild frostbite can leave lasting changes. A study of nearly 400 Norwegian soldiers who had experienced first- or second-degree frostbite found that 70% reported long-term symptoms, and 21% were unable to work or participate in their usual activities because of them. In another study following patients for 4 to 11 years after second-degree frostbite, 63% still had symptoms of some kind.
The most common long-term problem is cold sensitivity. Your body essentially overreacts to cold temperatures in the previously injured area, triggering vasospasm (sudden narrowing of blood vessels) that causes pain, numbness, and color changes in the skin. In one group of patients followed for four years, every single person with frostbitten feet still reported cold sensitivity, and 100% experienced a persistent cold sensation in the affected area.
Chronic pain is another frequent outcome. In a study of 14 frostbite patients, half reported ongoing pain, with 15% describing it as daily and intolerable. Half said frostbite had limited their social lives, and over a third reported poor emotional well-being years later. Nerve damage can cause persistent tingling, burning, or excessive sweating in the affected areas. Cold-induced arthritis in the joints of previously frostbitten fingers or toes is also well documented, sometimes appearing months or even years after the original injury.
These long-term effects also create a vicious cycle: the vasospasm and cold sensitivity make previously frostbitten tissue more vulnerable to refreezing in future cold exposures, which is why people who’ve had frostbite once need to be especially careful going forward.