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Introduction to Psoriasis and Scaling Diseases

By Shinjita Das, MD, Instructor in Dermatology; Assistant in Dermatology, Harvard Medical School; Massachusetts General Hospital

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.