Psoriasis Psoriasis Psoriasis is a chronic, recurring disease that causes one or more raised, red patches that have silvery scales and a distinct border between the patch and normal skin. A problem with the immune... read more , parapsoriasis Parapsoriasis Parapsoriasis refers to a group of skin diseases characterized by small and red or scaly patches on the skin. Parapsoriasis is not a type of psoriasis. It is so-named because it causes scaly... read more , pityriasis rosea Pityriasis Rosea Pityriasis rosea is a disease that causes the formation of many small patches of scaly, rose-colored or tan-colored patches on the skin. Pityriasis rosea may be caused by a viral infection.... read more , pityriasis rubra pilaris Pityriasis Rubra Pilaris Pityriasis rubra pilaris is a rare chronic skin disorder that causes thickening and yellowing of the skin, including the palms and soles, and red, raised bumps. The bumps may merge together... read more , lichen planus Lichen Planus Lichen planus, a recurring itchy disease, starts as a rash of small, separate, red or purple bumps that then combine and become rough, scaly patches. The cause is unknown but may be a reaction... read more , and lichen sclerosus Lichen Sclerosus Lichen sclerosus is a disorder that tends to cause itching and can cause scarring in the area around the anus and genitals. The cause of lichen sclerosis is unknown, but it may involve the immune... read more 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.