ELI5: Why do people with suffering from extreme anorexia have such terrible body odor?

This is a personal observation. It's not their breath. It's... them. Its like their skin smells bad. Let me clarify that I know this because I've helped a few friends in this situation and I've hugged them to comfort them only to find a unified stench between them all. I'd never mention it, but man, it is putrid.

EDIT: And I messed up the title. God damn it.