Necrosis of entire skin thickness and variable thickness of underlying subcutaneous tissue is:
1st degree frostbite is hyperemia and edema of skin.
2nd degree frostbite is hyperemia, vesicle formation and partial thickness necrosis of skin.
3rd degree frostbite is necrosis of entire skin thickness and variable thickness of underlying subcutaneous tissue.

4th degree frostbite is necrosis of entire thickness of skin and all underlying structures, leading to gangrene of the affected part.
1st degree frostbite
2nd degree frostbite
3rd degree frostbite
4th degree frostbite