From Lost Fables Wiki
Summoned from the Celestial Conclave
Non-transferrable. They will not leave their host, once they’ve been implanted.
Many celestials carry a sack of these mites in case they encounter a mortal in their realm in need of immortalization.
Preservation Mites are an odd form of Celestial indeed. Taking the form of near-microscopic mites the size of motes of dust, they actually have almost no deleterious effects on their hosts. Indeed, in the Celestial Conclaves, where they are directly connected to the power of Alchadiel, they have no negative effects whatsoever, imparting endless youth and life onto whoever they infest. It is only when they are on the Material Plane, only tenuously connected to the Truths which sustain them, that they begin to pose a problem for their host. The upside is that they keep their host youthful for the entire duration of their life, the downside is that they use the very energy of their host’s soul to power the revitalizing magics that they use. While the host stays young, their soul withers away, slowly ticking away their lifespan, and generally reducing the subject’s total lifespan by twenty percent or so. When they reach the end of this duration, they simply turn to dust, as if they had expended their entire soul using powerful magics. As an aside, a person infested with these mites cannot learn or use Truths, forgetting any that they knew coming into the procedure. In order to be infected by these things, the person must undergo a short ritual, whereby small incisions are made in both palms, both ankles, in front of the stomach, heart, and finally at the base of the skull. A small amount of the mites are poured into each incision, and when the final implantation of mites is done, the wounds immediately heal themselves as the mites fuse with the person’s soul and go to work.
This infestation is generally viewed as benign.
Thought to be irreversible, though there is likely a demon which can reverse it.