Blister
A blister was a painful skin condition where fluid filled a space between layers of skin.
In 2374, when Chakotay asked Rafin about the Kradin, Rafin described them with their flesh being gnarled and blistery like the rotting trunks. (VOY: "Nemesis")
In a deleted scene from ENT: "Broken Bow", Hoshi Sato asked Malcolm Reed what the symptoms of frostbite were. He told her "your appendages blister, peel and turn gangrenous."