A chronic recurrent rash due to inflammation characterized by small, flat-topped, many-sided (polygonal) bumps that can grow together into rough, scaly plaques on the skin. There may also be a rash in the lining (mucous membranes) of the mouth or vagina. The name Lichen is descriptive in that it resembles a simple plant, a lichen, that grows on rocks and tree bark, while planus is Latin for flat. It is an autoimmune disease. Many clinical variants exist that include atrophic, ulcerative, bullous, annular, linear, inverse, hypertrophic, lichen planopilaris, actinic LP and LP pigmentosus.
Here is a case I came across in which the disease precipitated under stress. The patient is cured of all the lesions now. Only a few marks are left which will also fade away with time.