Lichen planus is a chronic recurrent rash that is due to inflammation. The rash is 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.
Lichen planus is a very curious and poorly understood skin condition. Its name is descriptive in that to some it resembles a simple plant, a lichen, that grows on rocks and tree bark, while planus is Latin for flat.