This is my book I’ve always wanted to find again: it was I THINK a collection of sci-fi short stories, in one of which a character’s skin becomes translucent or transparent to the point that they can see all of their internal organs (which presumably remain as opaque as usual). At some point in the process of becoming translucent/transparent I think they went to live in a cave.
Lost Classics of Teen Lit: Name That Book! 
Probably ‘Undone!’ by Paul Jennings (1993), which has a story like this called “Clear as Mud.”
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