Definition of Lichen planus:

Lichen planus is a disease in which there is an itchy, swollen rash on the skin or in the mouth.

Causes, incidence, and risk factors:

The exact cause of lichen planus is unknown. However, it is likely to be related to an allergic or immune reaction.

Risks include:

• Exposure to medications, dyes, and other chemical substances (including gold, antibiotics, arsenic, iodides, chloroquine, quinacrine, quinide, phenothiazines, and diuretics)
• Disorders such as hepatitis C

Lichen planus generally affects middle-aged adults. It is less common in children.