Necrosis of the entire skin thickness and variable thickness of underlying subcutaneous tissue is:

1st degree frostbite is hyperaemia and edema of skin. 2nd degree frostbite is hyperaemia, vesicle formation and partial thickeness necrosis of skin.  3rd degree frostbite is necrosis of entire skin thickeness and variable thickeness of underlying subcutaneous tissue. 4th degree frostbite is necrosis of entire thickeness of skin and all underlying structures leading to gangrene of the affected part.