It's not anything. Because it doesn't exist.
People develop pathological scratching and textile fibres get into the wounds. That's it. Last I heard from the Morgellons community they were claiming the fibres were created by the disease. Clearly the laboratory findings that the fibres are all clothing textile fibres has now been absorbed into the mental pathology since it can't be explained away.
I mean, really. So-called scientific papers that cite anecdotes like
"However, a more thorough analysis of the fibers performed by the Federal Bureau of Investigation forensics laboratory has revealed that the fibers do not resemble textiles or any other manmade substance. In fact, the fibers are virtually indestructible by heat or chemical means, making analysis difficult by conventional methods.
Virtually indestructible fibres?? Surely the Government should be locking these people away and farming them to build a space elevator.
Oddly the incidence of this so-called disease is much lower in the UK, a country that mostly air-dries it's clothes. And isn't obsessed with alien abductions.