Marcus’s new body was rejecting his skin. Just like a snake or a transplant in reverse. Mother Nature's right hand hadn't squared things with her left. Marcus's new body was doing its best to dump his skin. It hadn't thought it smart to grow some more underneath first!
The body gave signals to the brain. “ERROR, ERROR, mismatch!... do something about it. Incompatible elements put together in a body fight, they rub each other up the wrong way. Where they meet is the battleground.
The weapon... extreme itching, not on the surface but down under the epidermis – skin deep.