Pathophysiology
The pathological mechanism by which frostbite causes body tissue injury can be characterized by four stages: Prefreeze, freeze-thaw, vascular stasis, and the late ischemic stage. Prefreeze phase: involves the cooling of tissues without ice crystal formation. Freeze-thaw phase: ice-crystals form, resulting in cellular damage and death. Vascular stasis phase: marked by blood coagulation or the leaking of blood out of the vessels. Late ischemic phase: characterized by inflammatory events, ischemia and tissue death. Diagnosis
Frostbite is diagnosed based on signs and symptoms as described above, and by patient history. Other conditions that can have a similar appearance or occur at the same time include:

Frostnip is similar to frostbite, but without ice crystal formation in the skin. Whitening of the skin and numbness reverse quickly after rewarming. Trench foot is damage to nerves and blood vessels that results exposure to wet, cold (non-freezing) conditions. This is reversible if treated early. Pernio or chilblains are inflammation of the skin from exposure to wet, cold (non-freezing) conditions. They can appear as various types of ulcers and blisters. Bullous pemphigoid is a condition that causes itchy blisters over the body that can mimic frostbite. It does not require exposure to cold to develop. Levamisole toxicity is a vasculitis that can appear similar to frostbite. It is caused by contamination of cocaine by levamisole. Skin lesions can look similar those of frostbite, but do not require cold exposure to occur.People who have hypothermia often have frostbite as well. Since hypothermia is life-threatening this should be treated first.
Oral or intravenous (IV) fluids should be given.Other considerations for standard hospital management include:

wound care: blisters can be drained by needle aspiration, unless they are bloody (hemorrhagic). Aloe vera gel can be applied before breathable, protective dressings or bandages are put on. antibiotics: if there is trauma, skin infection (cellulitis) or severe injury
tetanus toxoid: should be administered according to local guidelines. Uncomplicated frostbite wounds are not known to encourage tetanus. pain control: NSAIDs or opioids are recommended during the painful rewarming process. Rewarming
If the area is still partially or fully frozen, it should be rewarmed in the hospital with a warm bath with povidone iodine or chlorhexidine antiseptic. Active rewarming seeks to warm the injured tissue as quickly as possible without burning. The faster tissue is thawed, the less tissue damage occurs. According to Handford and colleagues, "The Wilderness Medical Society and State of Alaska Cold Injury Guidelines recommend a temperature of 37–39 °C, which decreases the pain experienced by the patient whilst only slightly slowing rewarming time." Warming takes 15 minutes to 1 hour. The faucet should be left running so the water can circulate. Rewarming can be very painful, so pain management is important. Medications
People with potential for large amputations and who present within 24 hours of injury can be given TPA with heparin. These medications should be withheld if there are any contraindications. Bone scans or CT angiography can be done to assess damage.Blood vessel dilating medications such as iloprost may prevent blood vessel blockage.