As freezing continues and penetrates deeper, intracellular freezing begins — ice crystals form inside the cells, causing direct mechanical damage to the cell membranes.

This damage is irreversible.

When the tissue thaws, the damaged cells release their contents, causing inflammation, fluid leakage (which produces the blisters that are characteristic of serious frostbite), and eventual cell death.

The depth of frostbite — how deeply into the tissue the freezing penetrates — determines the severity of the injury and the likelihood of tissue loss.

Superficial frostbite affects only the outer layers of skin.

Deep frostbite penetrates to muscle and bone, causing irreversible damage that requires amputation of the affected parts.