Frostbite is a term describing severe cold injury to the skin, soft tissue, and possibly deeper structures. Cold injury is most commonly seen in children, elderly individuals, mentally impaired individuals, substance abusers, distance and outdoor athletes in cold climates, and undomiciled persons without proper access to shelter or weather-appropriate clothing. Exposed areas such as the distal extremities, neck, chin, cheeks, nose, and ears are most often affected. Typically, the cold exposure occurs over minutes or hours, but even instantaneous exposure to cold metal can result in frostbite. At -2°C (28.4°F), cellular metabolism stops, proteins and enzymes are destroyed, and ice crystals form in the extracellular space, causing tissue damage and cell death.

Frostnip is the earliest sign of cold injury and presents with pain and pallor of the affected area, followed by numbness. With continued exposure, complete anesthesia will result. Many experts classify frostbite injuries as either superficial or deep, as this corresponds with a functional outcome. If a thumbprint may be left in the skin, the condition is more superficial, while deeper frostbite presents with skin that is hard to the touch. In deeper cases, deeper structures such as muscle, nerve, and bone may be affected.

The severity of tissue injury correlates with duration of exposure and lowest temperature. Pain and pruritus associated with frostbite can last as long as 8 weeks and 6 months, respectively. An increased sensitivity to cold may remain in areas of prior frostbite, and arthritis of acral joints may occur.

Predisposing factors for the development of frostbite include vascular conditions (such as peripheral vascular disease), diabetes, and the use of beta blockers. Additionally, peripheral neuropathy and Raynaud phenomenon, prolonged exposure to cold or high winds, restrictive clothing, and alcohol use predispose to frostbite. Prior damage from cold also increases the risk of frostbite. Athletes training at high altitude are at increased risk because of the combination of cold exposure and low ambient oxygen tension, which makes oxygen deprivation of affected tissues more severe.

Pediatric patient considerations: Children are at increased risk for frostbite because of their increased surface to body mass ratio. Younger children may not communicate symptoms at onset.