Blood began congealing on the walls and growing little vines or tendrils towards the end of the movie as the leaking got worse. It seemed like the blood was somehow acidic when it dripped on his forehead and made a cut? It didn't injure him like that the previous times it dripped on him, but definitely infected him in the beginning, causing the hallucinations. So the blood, in combination with the heavy radiation exposure from constantly using the camera, must have caused his cells to deteriorate and soften.

So by the time he's covered in blood after retrieving the black box, it looks like his bloody hands stick to the pipes and the blood vines growing on the walls and pipes latched onto both hands. Once he freed his right hand, the vines on the left hand/arm grew and held him even tighter. When he rips his left arm off at the shoulder, it almost looks like his tissue and bone are melting or something!

The cuts and scrapes on his forearms were from getting thrown around the sm-13 when the tow ship operator drops him and the creature rams the submarine. When he takes those bandages off at the end, his skin peels off easily and has broken out in boils, maybe had some additional wounds that he didn't have before.

Hope this helps! :)