In the movie Iron Man Tony Stark and Pepper Potts have this exchange when he switches to the Mark II chest piece.
Potts: Oh, there's pus!
Stark: It's not pus. It's an inorganic plasmic discharge from the device, not from my body.
Potts: It smells!
Stark: Yeah, it does.
When he wears the chest piece, the giant hole in his chest is sealed. Where does the inorganic plasmic discharge go? Does it just continue to build up inside his body? That can't be healthy.