(HealthDay News) -- Lichen planus is a rare, painful and recurrent itchy rash or lesion on the skin or in the mouth.
The exact cause isn't known but is thought to involve an allergic or immune reaction to a medication, dye or other chemical substance, such as glue for dentures.
Stress can make it worse, the U.S. National Library of Medicine says.
The condition usually occurs in middle age or later, and is rare in children.
Treatment may include an antihistamine, topical steroid, and even ultraviolet light.
