Lichen planus is a recurrent rash due to inflammation of the skin. The rash is characterized by small, flat-topped, many-sided, polygonal bumps that can grow together into rough, scaly patches on the skin. There may also be a rash in the mucous membranes of the mouth or vagina. Lichen planus is a skin condition, in which the effects are localized to the areas of involvement. (Lichen refers to a tree moss while planus is Latin for flat = like a flat tree moss.)

The major point of distinction of lichen planus from eczema, psoriasis, and other common rashes is its color -- lilac or violet. The textbooks call it "violaceous." Lichen planus itches with an intensity that varies in different people from mild to severe. The onset of lichen planus can be sudden or gradual. The first attack may last for weeks or months, and recurrences may happen for years. Children are not often affected by lichen planus. The bumps at first are 2 to 4 mm in diameter, with angular borders, and a violaceous color. At the onset of the disease, new bumps may appear at sites of minor skin injury, such as a superficial scratch. Hyperpigmentation may develop in the affected skin as the lesions persist. Rarely, a patchy scarring balding (loss of hair) of the scalp occurs. The appearance of lichen planus depends on whether the skin or the mucous membranes inside the mouth or vagina is affected: The usual skin involvement with lichen planus consists of flat-topped lilac or violet spots a few millimeters in diameter on the skin. These spots tend to be located on the inner wrists, forearms, the lower legs just above the ankles, and the lower part of the back. A variant of this disease is called hypertrophic lichen planus. This condition appears as thick, reddish-brown lesions that are covered with scales. These spots tend to be on the shins, but they can occur anywhere on the body. This is an especially itchy and chronic variety of lichen planus. Lichen planus of the mucous membranes is common. About half of the people affected with lichen planus have the rash inside of their mouths. The oral rash often occurs prior to any skin involvement. More troublesome, although rare, is erosive lichen planus, which can be quite sore and uncomfortable. This erosive form typically causes the patient to complain of the shallow and often quite painful, recurrent ulcers in the mouth. Lichen planus can affect the female genitals, including the vagina. This condition can be confused with sexually transmitted diseases (STDs), although lichen planus is neither sexually transmitted nor contagious. Sometimes, lichen planus produces pits and grooves in the nails as well.

Usually, lichen planus is relatively easy to diagnose. Physicians can make the diagnosis in typical cases simply by looking at the rash. If necessary, a skin biopsy may be done to confirm the diagnosis. Under the microscope, lichen planus is distinctive in appearance. This tell-tale appearance under the microscope can be valuable in ensuring that the rash or spots are lichen planus. Persistent oral or vaginal lichen planus, with spots that thicken and grow together, can sometimes be difficult to distinguish clinically from whitish precancerous plaques called leukoplakia. A biopsy can be helpful in this situation. Widespread lichen planus with erosions in the mouth can also be confusing. A biopsy may be required to distinguish this from other conditions such as candidiasis, cancer, and ulcers in the mouth.

In most cases, the cause of lichen planus is unknown. Some drugs, such as those containing arsenic, bismuth, or gold can cause a reaction that is indistinguishable from the rash of lichen planus. Exposure to certain chemicals used in the development of color photographs can also produce a similar rash. The long-term use of the drugs quinacrine or quinidine used for malaria, may produce hypertrophic lichen planus of the lower legs and other skin and systemic disturbances. Other unusual causes of lichen planus include liver disease and what is called graft-versus-host disease in people who have received a transplant.

The average duration of the condition is 4 years. Even after going away, lichen planus may recur. The disease is thus paradoxical in that it tends to be self-limiting but may recur after years. It is usually not associated with any systemic diseases or problems.

Lichen planus of the skin is generally noncancerous (benign). It may clear up with treatment but can persist for months to years. People with long-term lesions of the mucous membranes are at greater risk of squamous cell carcinoma â€" a form of skin cancer. In these cases, a doctor may advise regular examinations to monitor any changes in the skin. It's also important to stop any tobacco use because tobacco raises your risk of squamous cell carcinoma.

If you have lichen planus of the mucous membranes, treatment is often challenging and may take years. Measures that may help reduce the itching and inflammation caused by lichen planus are:

• Tub soaks with colloidal oatmeal


• Cool compresses