Immobility and physical stress (such as malnutrition or dehydration) are also risk factors. Disorders and substances that impair circulation contribute, including diabetes, Raynauds phenomenon, tobacco and alcohol use. Homeless individuals and individuals with some mental illnesses may be at higher risk. Mechanism
Freezing
In frostbite, cooling of the body causes narrowing of the blood vessels (vasoconstriction). Temperatures below −23 °C (−9 °F) are required to form ice crystals in the tissues. The process of freezing causes ice crystals to form in the tissue, which in turn causes damage at the cellular level. Ice crystals can damage cell membranes directly. In addition, ice crystals can damage small blood vessels at the site of injury. Scar tissue forms when fibroblasts replace the dead cells. Rewarming
Rewarming causes tissue damage through reperfusion injury, which involves vasodilation, swelling (edema), and poor blood flow (stasis). Platelet aggregation is another possible mechanism of injury. Blisters and spasm of blood vessels (vasospasm) can develop after rewarming. Non-freezing cold injury
The process of frostbite differs from the process of non-freezing cold injury (NFCI). In NFCI, temperature in the tissue decreases gradually. This slower temperature decrease allows the body to try to compensate through alternating cycles of closing and opening blood vessels (vasoconstriction and vasodilation). If this process continues, inflammatory mast cells act in the area. Small clots (microthrombi) form and can cut off blood to the affected area (known as ischemia) and damage nerve fibers. Rewarming causes a series of inflammatory chemicals such as prostaglandins to increase localized clotting.
Grades
Grade 1: if there is no initial lesion on the area, no amputation or lasting effects are expected
Grade 2: if there is a lesion on the distal body part, tissue and fingernails can be destroyed
Grade 3: if there is a lesion on the intermediate or near body part, auto-amputation and loss of function can occur
Grade 4: if there is a lesion very near the body (such as the carpals of the hand), the limb can be lost. Sepsis and/or other systemic problems are expected.A number of long term sequelae can occur after frostbite. These include transient or permanent changes in sensation, paresthesia, increased sweating, cancers, and bone destruction/arthritis in the area affected. Epidemiology
There is a lack of comprehensive statistics about the epidemiology of frostbite. In the United States, frostbite is more common in northern states. In Finland, annual incidence was 2.5 per 100,000 among civilians, compared with 3.2 per 100,000 in Montreal. Research suggests that men aged 30–49 are at highest risk, possibly due to occupational or recreational exposures to cold. History
Frostbite has been described in military history for millennia. The Greeks encountered and discussed the problem of frostbite as early as 400 BCE. Researchers have found evidence of frostbite in humans dating back 5,000 years, in an Andean mummy. Napoleons Army was the first documented instance of mass cold injury in the early 1800s. According to Zafren, nearly 1 million combatants fell victim to frostbite in the First and Second World Wars, and the Korean War.