Lichen planus is a disease of the skin/mucous membranes that resembles lichen. The cause is unknown, but it is thought ot be the result of an autoimmune process with an unknown initial trigger. There is no cure, but many different drugs and procedures have been used to control Sx. Lichenoid reaction (aka lichenoid lesion) is a lesion of similar or identical histopathologic and clinical appearance to lichen planus, i.e. an area which looks the same as lichen planus, both to the naked eye and under a microscope. Sometimes, dental materials or certain drugs can cause a lichenoid reaction. It can also occur in association with GvHD.

Variants of cutaneous lichen planus include:

• Lichen planus pemphigoides
• Keratosis lichenoides chronica (aka Nekahm's disease)
• Lichenoid keratoses (aka benign lichenoid keratosis, solitary lichen planus)
• Lichenoid dermatitis