Frostbite is freezing of the skin and tissues below the skin. It occurs when a person is exposed to freezing temperatures [ 0°C (32°F)] or lower for too long.

How severe the frostbite is depends on how long the person was exposed to cold, the temperature, the wind chill, and the humidity. Frostbite is most likely to occur on the feet, hands, ears, nose, and face. Men may have frostbite of the genitals if they do not dress properly.

Doctors rate frostbite by degree of severity:

First-degree frostbite

First-degree frostbite freezes part of the outer layer of skin. Symptoms include:

• Tingling, stinging, or burning pain.
• Red skin or, less often, white, yellow, or pink-blue skin.
• Mild swelling.
• No blisters.

Second-degree frostbite

Second-degree frostbite is freezing of all layers of the skin. Symptoms include:

• Numbness followed by aching and throbbing pain.
• Hard and frozen outer skin.
• Blisters filled with clear or milky fluid. Blisters form within 6 to 24 hours.
• Red, swollen skin around blisters.

Third-degree frostbite

Third-degree frostbite is freezing of deep layers of skin and tissues below the skin. Symptoms include:

• White, pink-purple, or blue-grey skin.
• Hard and frozen skin that "feels like a block of wood."
• Blisters that look like they are filled with blood.
• Numbness followed by burning, throbbing, or shooting pain.

Fourth-degree frostbite

Fourth-degree frostbite is freezing of muscles, tendons, and bones. Symptoms include:

• Patches of red or blue skin that turn dry, black, rubbery.
• Little or no swelling.
• Blisters that may appear as small blood spots under the skin.
• Deep, aching joint pain.

Pain may be severe as the frostbitten skin rewarms. Swelling and blisters are common after rewarming.

Medical treatment for frostbite includes relieving pain and quickly rewarming the frostbitten area. This can help prevent problems such as infection, dead tissue, or amputation of the frozen part.