First degree
First degree frostbite is superficial, surface skin damage that is usually not permanent. Early on, the primary symptom is loss of feeling in the skin. In the affected areas, the skin is numb, and possibly swollen, with a reddened border. In the weeks after injury, the skins surface may slough off. Second degree
In second degree frostbite, the skin develops clear blisters early on, and the skins surface hardens. In the weeks after injury, this hardened, blistered skin dries, blackens, and peels. At this stage, lasting cold sensitivity and numbness can develop. Third degree
In third degree frostbite, the layers of tissue below the skin freeze. Symptoms include blood blisters and "blue-grey discoloration of the skin". In the weeks after injury, pain persists and a blackened crust (eschar) develops. There can be longterm ulceration and damage to growth plates. Fourth degree
In fourth degree frostbite, structures below the skin are involved like muscles, tendon, and bone. Early symptoms include a colorless appearance of the skin, a hard texture, and painless rewarming. Later, the skin becomes black and mummified. The amount of permanent damage can take one month or more to determine. Autoamputation can occur after two months. Causes
Risk factors
The major risk factor for frostbite is exposure to cold through geography, occupation and/or recreation. Inadequate clothing and shelter are major risk factors. Frostbite is more likely when the bodys ability to produce or retain heat is impaired. Physical, behavioral, and environmental factors can all contribute to the development of frostbite.
Technetium-99 or MR scans are not required for diagnosis, but might be useful for prognostic purposes. Prevention
The Wilderness Medical Society recommends covering the skin and scalp, taking in adequate nutrition, avoiding constrictive footwear and clothing, and remaining active without causing exhaustion. Supplemental oxygen might also be of use at high elevations. Repeated exposure to cold water makes people more susceptible to frostbite. Additional measures to prevent frostbite include:
Avoiding temperatures below −23 °C (-9 °F)
Avoiding moisture, including in the form of sweat and/or skin emollients
Avoiding alcohol and drugs that impair circulation or natural protective responses
Layering clothing
Using chemical or electric warming devices
Recognizing early signs of frostnip and frostbite

Treatment
Individuals with frostbite or potential frostbite should go to a protected environment and get warm fluids. If there is no risk of re-freezing, the extremity can be exposed and warmed in the groin or underarm of a companion. If the area is allowed to refreeze, there can be worse tissue damage. If the area cannot be reliably kept warm, the person should be brought to a medical facility without rewarming the area. Rubbing the affected area can also increase tissue damage. Aspirin and ibuprofen can be given in the field to prevent clotting and inflammation. Ibuprofen is often preferred to aspirin because aspirin may block a subset of prostaglandins that are important in injury repair.The first priority in people with frostbite should be to assess for hypothermia and other life-threatening complications of cold exposure. Before treating frostbite, the core temperature should be raised above 35 °C.