Lichen planus is a condition that forms an itchy rash on the skin or in the mouth.

The exact cause of lichen planus is unknown. It may be related to an allergic or immune reaction.

Risks for the condition include:

• Exposure to medicines, dyes, and other chemicals (including gold, antibiotics, arsenic, iodides, chloroquine, quinacrine, quinide, phenothiazines, and diuretics)
• Diseases such as hepatitis C

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

Mouth sores  

• May be tender or painful (mild cases may not cause plain)
• Are located on the sides of the tongue, inside of the cheek, or gums
• Look like blue-white spots or "pimples"
• Form lines in a lacy network
• Gradually increase in size of the affected area
• Sometimes form painful ulcers

Skin sores

• Are usually found on the inner wrist, legs, torso, or genitals
• Are itchy
• Have even sides (symmetrical) and sharp borders
• Occur in single lesion or clusters, often at the site of skin injury
• May be covered with thin white streaks or scratch marks (called Wickham's striae)
• Are shiny or scaly looking
• Have a dark, reddish-purple color on the skin or are gray-white in the mout
• May develop blisters or ulcers

Other symptoms:

• Dry mouth
• Hair loss
• Metallic taste in the mouth
• Ridges in the nails (nail abnormalities)

The health care provider may make the diagnosis based on the appearance of the skin or mouth lesions.

A skin lesion biopsy or biopsy of a mouth lesion can confirm the diagnosis. Blood tests may be done to rule out hepatitis.

The goal of treatment is to reduce symptoms and speed healing. If symptoms are mild, you may not need treatment.

Treatments may include:

• Antihistamines
• Medicines that calm down the immune system, such as cyclosporine (in severe cases)
• Lidocaine mouthwashes to numb the area and make eating more comfortable (for mouth sores)
• Topical corticosteroids (such as clobetasol) or oral corticosteroids (such as prednisone) to reduce swelling and lower immune responses
• Corticosteroids shots into a sore
• Vitamin A as a cream (topical retinoic acid) or taken mouth (acitretin)
• Other medicines that are applied to the skin such as tacrolimus and pimecroliumus
• Dressings  placed over skin medicines to protect from scratching
• Ultraviolet light therapy for some cases

Lichen planus is usually not harmful. It usually gets better with treatment. The condition often clears up within 18 months but may come and go for years.

If lichen planus is caused by a medicine you are taking, the rash should go away once you stop the medicine.

Mouth ulcers that are present for a long time may develop into oral cancer.

Call your health care provider if:

• Your symptoms continue
• The skin or mouth lesions change in appearance
• The condition continues or worsens even with treatment
• Your dentist recommends changing your medicines or treating conditions that trigger the disorder

In: James WD, Berger TG, Elston DM, eds. Andrews'Diseases of the Skin: Clinical Dermatology. 11th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 12

Mirowski GW, Mark LA. Oral disease and oral-cutaneous manifestations of gastrointestinal and liver disease. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elseiver;2010:chap 22.