Frostbite

What is it?

Frostbite is the freezing of body tissues (skin, muscle, bone) in extreme cold. At or below 59 degrees Fahrenheit, blood vessels close to the skin start to narrow (constrict). This helps to preserve your core body temperature. In extreme cold or when the body is exposed to cold for long periods, this protective strategy can reduce blood flow in some areas of your body to dangerously low levels. The combination of cold temperature and poor blood flow can cause tissue injury. Frostbite is most likely to happen in body parts farthest from the heart, and those with a lot of surface area exposed to cold. These areas include the toes, fingers, ears and nose.

Body tissue will not freeze until the outside temperature is at or below 28 degrees Fahrenheit. If areas of tissue exposed to extreme cold begin to freeze, ice crystals form in some cells and fluid flows into these cells. This can cause the cells to burst. Additional damage can occur when the tissue is warmed again, because damaged blood vessels can leak fluid and proteins into tissue, causing swelling and blistering.

Frostbite ranges from the superficial freezing of the topmost layers of skin, which is called frostnip, to severe frostbite that affects deeper tissues, such as muscles and bones. The amount of damage depends on several factors besides the cold temperature, including altitude, wind chill, blood circulation and body composition. Factors that increase your risk of frostbite include:

immobility
impaired thinking (from psychiatric problems, medical illness, or substance abuse)
older age, especially if you already have circulation problems
wet skin
contact with metal
large areas of exposed skin
previous frostbite or other injury caused by cold
a low percentage of body fat
dehydration
wearing tight clothes, which impairs circulation
drinking alcohol, which increases loss of body heat
drinking caffeine, which increases dehydration
using nicotine, which decreases blood flow to your limbs
poorly controlled diabetes.

Symptoms

In frostnip, the skin may feel numb or normal. It looks waxy and white, or lighter than usual. Frostnip is common on the toes, earlobes, cheeks and fingers. When the skin is warmed after frostnip, it may turn red.

In mild frostbite, the tissue is numb and feels soft. It looks lighter than normal, or even white. Blistering can occur. As frostbite progresses, or after the injured skin is warmed, the skin may be more pink or red than usual.

In deep frostbite, the skin is numb and feels hard, like wood. It looks pale or white. At this point, muscle and bone may be frozen. In more severe cases of frostbite, the skin can turn blue, gray or even black because of tissue injury. These changes sometimes don't happen until after the area is warmed.

Diagnosis

Doctors diagnose frostbite by examining the skin. Distinguishing mild frostbite from deep frostbite can be difficult before the skin is thawed. If clear blisters form within 48 hours of thawing, you have mild frostbite. If blisters filled with blood or cloudy fluid form more than 48 hours after thawing, you have deeper frostbite.

Expected duration

There may not be any permanent tissue damage in mild cases of frostbite. The most severe cases may require amputation. Each case of frostbite is slightly different.

Prevention

The easiest way to prevent frostbite is to avoid exposure to cold.

If you must be outside in cold temperatures, you can protect yourself in several ways:

Dress in loose layers of clothing. The outermost layer should be wind-resistant to reduce heat loss. Inner layers of silk, polypropylene or wool will keep you warmer than cotton.
Stay dry. If you are skiing or snowshoeing and are perspiring, remove wet layers of clothing or wear layers that wick moisture away from your skin.
Try not to go out alone. If you are out in the cold with someone else, you can check each other periodically for signs of frostbite.
If you start to shiver, go inside if possible.
Do not handle liquid fuel, such as gasoline. At cold temperatures, fuel can drop below its freezing point yet remain in liquid form. If it touches your skin, it will evaporate immediately and can lead to instant frostbite.
Wear protective eyewear. It is possible for your corneas to become frostbitten, especially in cold, windy conditions.

Treatment

To treat frostnip or mild frostbite, gently blow air on the area or place it against a warmer area of the body. For example, place your fingers in your armpit or your palms against your ears, or place your fingers between someone else's hands.

If you experience serious frostbite, see a doctor or go to an emergency room as soon as you can. If this is not possible, begin to warm the body part before visiting a doctor. However, it's best to warm frostbitten areas under medical supervision to minimize tissue damage. Also, because the frostbitten area can be painful as it thaws, a doctor's office or hospital can give you pain medicines to reduce the discomfort.

If a person with frostbite has a lower-than-normal body temperature (hypothermia), the frostbite can only be treated safely once the core body temperature has been restored to normal. This usually is done by removing the person's wet clothing and covering the person with warm blankets, but it may require emergency medical care. Frostbitten parts may then be immersed in water that is heated to between 104 degrees Fahrenheit to 108 degrees Fahrenheit for 15 to 30 minutes. When color and sensation return and the skin feels normal, the area has thawed.

After thawing, the affected area should be dried, wrapped in gauze and protected from friction. If you have thawed fingers and toes, use gauze or other padding to separate them from one another. The thawed part is likely to swell and blister. It is best to leave blisters intact.

Severe frostbite can cause deep tissue death, also called gangrene. Gangrene can cause the injured part to deteriorate enough that part or all of the finger or toe, or part of an arm or leg, is lost. Some severe frostbite injuries require skin grafting or surgical amputation.

To warm frostbitten corneas, place your hands over your eyes or cover them with a warm compress. If you think your corneas may have been injured, visit a doctor. After warming, the eyes will need to be covered with gauze or a patch for one to two days.

Some attempts at treatment can actually damage tissues. To protect against damage, take these precautions:

Do not massage the body part or rub snow on it.
Do not use water warmer than 110 degrees Fahrenheit to warm the body part.
Do not use dry heat, such as a radiator or hair dryer, to warm the body part.
Do not thaw a body part if there is a chance it may freeze again. Keeping the part frozen for several hours will not cause further damage, but warming and refreezing will.
Do not immerse a person's arm or leg in a warming bath if you suspect they may have hypothermia (a low, core body temperature). Hypothermia can cause symptoms such as a fast breathing rate, a fast pulse, confusion, balance or speech difficulties, or shivering.

Once the skin has thawed, your doctor may recommend further treatment, including blood-thinning medication, anti-inflammatory drugs, pain relievers and antibiotics. In some cases, your doctor or a surgeon may remove some of the dead tissue. You may need to keep the arm or leg elevated, and your doctor may recommend that you use an ointment, such as aloe vera.

When to call a professional

If your skin is painful, gray or blue, hard to the touch, blistered or extremely swollen, contact your doctor or visit an emergency room.

If you are treating yourself for frostbite and notice blisters or dark blue or black areas under your skin, see your doctor immediately.

Prognosis

Frostnip or mild frostbite usually has an excellent prognosis, with no complications. Deep frostbite can lead to amputation. Infection may complicate frostbite and cause even more tissue death, and it can be life threatening.

Additional info

Centers for Disease Control and Prevention (CDC)
https://www.cdc.gov/