This disease had almost killed Rygel XVI many cycles ago, and still resided dormant in his body until reactivated by Utu-Noranti Pralatong on board a Scarran border station to distract the Scarrans so Moya's crew could escape. Although Noranti managed to find a cure to save Rygel, she was unable to help the Kalish on board the station in time, and many died because of it.
Dermafollica started with symptoms of wooziness, nausea, and extreme vomiting. It developed quickly, causing the victim's skin to slough off in enormous quantities, and was soon fatal. Noranti had only a solar day or two to concoct a remedy for Rygel before the dermafollica became irreversible.
Also according to Noranti, dermafollica was caused by a bacteria that stimulated the dermafollica virus to reproduce. ("We're So Screwed - Fetal Attraction")