Elastic-Skin, India Rubber-Skin, Blue Men, Human Slates
"India Rubber Skin" men (and some women), generally suffered from Ehlers–Danlos Syndrome, an inherited connective tissue disorder that allows the skin to be stretched in different directions. EDS is caused by a defect in the structure, production, or processing of collagen in the skin, and produces dramatic results in those that suffer from the affliction.
Note that some acts billed as "India Rubber Man" were actually contortionists, and were not skin stretchers, but stretchers of limbs.
Other similar skin anomalies such as Human Slates whose skin is so sensitive that dragging a finger across it leaves markings, and Blue Men whose skin has been modified and colorized by ingestion of silver extract, also fit uneasily into this sub-heading.
Fickling, William Z. "The Human Slate" [blk 0-366]
Haig, "Elastic Skin Man" [ajax101]
Knotty Man, The
Loos, Arthur
Nels Nelson [e]
Roland, F.C. "India Rubber Man"
Rubber Neck Harry [ajax101]
Rubber Nelson
Spanner, Peter "Rubber-Skin" [mm123, ss15]
Schmidt, Agnes C. "Rubber Skinned Woman"