Psoriasis, parapsoriasis, pityriasis rosea, pityriasis rubra pilaris, lichen planus, and lichen sclerosus are different skin disorders that have been grouped together because the bumps, rashes, scales, and skin discoloration they cause have similar characteristics. That is, the rashes and bumps have well-defined borders, and the scales usually do not crust, crack, or weep with fluid.
Doctors tell these disorders apart by examining the bumps, rashes, scales, and skin discoloration and noting where they appear on the skin.
