What is the X in X-mas?
1680s, from medical Latin psoriasis, in Late Latin "mange, scurvy," from Greek psoriasis "being itchy," from psorian "to have the itch," from psora "itch, mange, scab," related to psen "to rub" (see psilo-). Related: Psoriatic.
psoriasis pso·ri·a·sis (sə-rī'ə-sĭs)
A noncontagious inflammatory skin disease characterized by recurring reddish patches covered with silvery scales.