Suction blister formation in human skin is preceded by intra-epidermal vacuolation, which regresses as the blister forms. The vacuoles are shown to contain fluid, not gas, and probably represent a reaction to injury by suction accompanied by increased permeability of epidermal structures.
Comaish S. Instantaneous Decompression and the Skin. Arch Dermatol. 1973;108(2):215-217. doi:10.1001/archderm.1973.01620230015005