Greyskins, or Carriers, are servants of the Choir. Their mocking name comes from the fact that their entire

"Please, don't look at me"

body is covered, head to toe, with the mossy, moldish substance that is their horrid master. 

Constantly tortured by the whisperings of the Choir in their ear, the Greyskin will close themselves off from humanity, from society, not contacting anyone unless the Greyskin would die otherwise. 

Greyskins take several years to die from the infection, however, luckily for the Choir, as it only reaches its mature, spreading form, when the victim dies, most Greyskins will go utterly insane, shooting themselves or hanging themselves, sometimes trying to take others with them.

Contact with the form of the Choir which can infect does not guarantee infection, nor does it even mean infection will occur shortly after contact. Sometimes, an infection will form decades after contact. The Choir will attack and infect only if a person is so utterly unsure of themselves, so dependant on what others think of them, that their lives revolve around pleasing others, even unto the point of harming themselves.