As of 2015, the cause of oral lichen planus is unclear, according to Mayo Clinic. However, since the condition somehow activates the T lymphocytes that cause inflammation, factors that trigger an inflammation illness such as allergens, a hepatitis C infection and nonsteroidal anti-inflammatory may also trigger oral lichen planus.
Oral lichen planus is an autoimmune disorder that attacks the mucous membranes of the mouth, explains Mayo Clinic. It is not contagious and shows as patches, open sores and swollen tissue in the mouth. Though the symptoms are controllable, they need constant monitoring as the condition may develop into mouth cancer.