Ninety percent of cases in Brazil occur in rural areas near water. Patients removed from the rural environment improve, but relapse when returned to the original areas. A tribe of natives is being watched in a remarkable study. These natives were relocated to an area in which Fogo Selvagem is common. They were evaluated medically before they moved and are being visited often in the five years of the study.
Some patients have pemphigus antibodies up to five years before the first sign of blistering.
No medical personnel in contact with FS patients have ever developed the disease. Paraneoplastic pemphigus is the most problematic of the subsets. It affects the mucous membranes, palms, soles of the feet, lips and some internal organs. It is always associated with one of several uncommon tumors of the immunologic or blood systems. Pemphigoid was differentiated from pemphigus in the 1950s.