Pityriasis rosea: This common skin disease causes patches on the skin. Your dermatologist may call the large patch a mother patch. The smaller patches are daughter patches. Pityriasis rosea: Overview Pityriasis rosea: This common skin disease causes patches on the skin. Your dermatologist may call

  Lichen planus: This common skin disease often develops on the wrist. Lichen planus: Overview Many people get lichen (LY-kin) planus (PLAN-us). This disease can develop on one or several parts of the body. It can appear on the skin or inside the mouth. Sometimes, it appears in both places. Lichen