Lichen planus is a condition that affects the hair, skin, nails and the mucous membranes of the body. It is usually seen as itchy, flat, purplish bumps on the skin. In the vagina, mouth and other areas covered by mucous membranes, lichen planus forms lacy white patches, with painful sores in some cases. Depending on the severity of the condition, the lesions can appear and spread over a course of several weeks.