Rabbi Lavery-Yizraeli writes that tzara’at is not a medical condition, even though it seems like it is. Only the Kohen diagnoses, and a Kohen cannot diagnose for himself. In fact, without a qualified Kohen, the tzara’at cannot exist, because it requires the Kohen’s declaration. Slander is actually considered to be the cause of it, rather than another type of exposure. Read the article