Frostbite is an injury to skin or other living tissue that is allowed to freeze, especially affecting the fingers, toes, nose, ears, cheeks and chin. Most often, frostbite occurs in the hands and feet, often preceded by frostnip, a paling or reddening of a body part as its blood vessels constrict that tingles, feels very cold, or simply feels numb. This may be followed by the clumsiness and white or bluish, waxy-looking skin that evidence full-blown frostbite. Swelling or blistering may occur following treatment. Complications may include hypothermia or compartment syndrome.

Frostbite
Other names	Frostnip
Frostbitten toes two to three days after mountain climbing
Specialty	Dermatology, emergency medicine, orthopedics
Symptoms	Numbness, feeling cold, clumsiness, pale color
Complications	Hypothermia, compartment syndrome
Types	Superficial, deep
Causes	Temperatures below freezing
Risk factors	Alcohol, smoking, mental health problems, certain medications, prior cold injury
Diagnostic method	Based on symptoms
Differential diagnosis	Frostnip, pernio, trench foot
Prevention	Avoid cold, wear proper clothing, maintain hydration and nutrition, stay active without becoming exhausted
Treatment	Rewarming, medication, surgery
Medication	Ibuprofen, tetanus vaccine, iloprost, thrombolytics
Frequency	Unknown

People who are exposed to low temperatures for prolonged periods, such as winter sports enthusiasts, military personnel, and the homeless, are at greatest risk. Other risk factors include drinking alcohol, smoking, mental health problems, certain medications, and prior injuries due to cold. The underlying mechanism involves injury from ice crystals and blood clots in small blood vessels following thawing. Diagnosis is based on symptoms. Severity may be divided into superficial (first and second degree) and deep (third and fourth degree). A bone scan or MRI may help in determining the extent of injury.

Prevention consists of wearing proper, fully-covering clothing, avoiding low temperatures and wind, maintaining hydration and nutrition, and sufficient physical activity to maintain core temperature without exhaustion. Treatment is by rewarming, immersion in warm water (near body temperature), or body contact, and should be done only when a consistent temperature can be maintained so that refreezing is not a risk. Rapid heating or cooling should be avoided since it could potentially cause burning or heart stress. Rubbing or applying force to the affected areas should be avoided as it may cause further damage such as abrasions. The use of ibuprofen and tetanus toxoid is recommended for pain relief or to reduce swelling or inflammation. For severe injuries, iloprost or thrombolytics may be used. Surgery, including amputation, is sometimes necessary.

Evidence of frostbite occurring in humans dates back 5,000 years. Evidence was documented in a pre-Columbian mummy discovered in the Andes. The number of annual cases of frostbite is unknown. Rates may be as high as 40% a year among those who mountaineer. The most common age group affected is those 30 to 50 years old. Frostbite has also played an important role in a number of military conflicts. Its first formal description was in 1813 by Dominique Jean Larrey, a physician in Napoleon's army, during its invasion of Russia. Frostbite reports were largely military until the late 1950s.