What is lichen planus? Causes, symptoms and treatment

What is lichen planus?

Lichen planus is a chronic, inflammatory skin disease thought to be an autoimmune reaction. The body's own immune system attacks skin cells, triggering inflammation and the characteristic rash pattern.

The condition can affect the skin, oral lining, genitals, scalp and nails. There is no cure, but treatment can calm the inflammation, relieve the itch and — most importantly — prevent permanent scarring on the scalp and in the genital area.

Is lichen planus contagious?

No. Lichen planus is not contagious. It is not an infection, and it cannot be passed on by touch, kissing, sex or sharing towels. You cannot give it to your child or your partner either, even when the rash is in the mouth or on the genitals.

What does lichen planus look like?

Lichen planus on the skin is classically described by the six Ps:

• Purple: The colour is characteristically dark red to violet.
• Polygonal: The bumps have straight, angular sides rather than being round.
• Planar (flat-topped): The top surface is flat and slightly shiny, as though the bump had been sliced off.
• Pruritic (itchy): Intense itching is one of the most prominent symptoms.
• Papules: Small, raised bumps that may be solitary or grouped.
• Plaques: Individual papules can merge into larger, thickened patches — especially on the shins.

Another characteristic feature is Wickham striae — fine, white, lace-like lines on the surface of the bumps. These lines are often visible when the affected area is examined with a magnifying glass.

The rash typically sits symmetrically on the wrists, forearms, ankles and lower back. New bumps can appear along a scratch or a scar — this is called the Köbner phenomenon — and when the bumps clear they often leave dark brown marks that can take months to fade.

Which other parts of the body can lichen planus affect?

The mouth (oral lichen planus)

In the mouth, lichen planus most often appears as white, lace-like patterns on the inside of the cheeks, which rarely hurt. In the erosive and atrophic forms, however, there are red, sore areas and open ulcers that can make it difficult to eat spicy or acidic food.

The scalp (lichen planopilaris)

When lichen planus affects the scalp it is called lichen planopilaris. The inflammation destroys the hair follicles, and hair lost to that scarring does not grow back. Treatment can halt further loss but cannot restore what has already gone. That is why patchy hair loss with redness, itching or scaling around the hair openings needs prompt assessment.

The genitals (erosive lichen planus)

In the genital area, lichen planus can take an erosive form. Erosive vulvovaginal lichen planus causes raw, painful areas that scar as they heal, and over time that scarring can fuse the labia and narrow or close the vagina. As on the scalp, the damage is permanent once it has happened, so persistent soreness, pain during sex or unexplained discharge should be examined rather than treated as thrush. Men can develop the equivalent erosive form on the glans.

The nails

Nail involvement occurs in around one in ten people and causes lengthwise ridges, thinning and, in severe cases, complete loss of the nail plate. Here too the damage can become permanent if the inflammation is allowed to continue.

Why does lichen planus happen?

The exact cause is unknown, but several factors are thought to be able to trigger the autoimmune reaction:

An autoimmune reaction

Research suggests that T-lymphocytes (a type of white blood cell) attack skin cells in an attempt to remove something they perceive as foreign — even though there is no actual foreign substance present.

Medicines (lichenoid drug eruption)

A lichenoid drug eruption looks almost identical to lichen planus but is caused by a medicine. The drugs most often involved are ACE inhibitors, thiazide diuretics, beta-blockers, antimalarials such as hydroxychloroquine, gold, penicillamine, NSAIDs and the anti-PD-1 checkpoint inhibitors used in cancer treatment. The rash can start months after the drug is begun and can take months to settle after it is stopped. Dental amalgam can trigger oral lichen planus where the filling touches the mucosa.

Hepatitis C

There is a documented association between hepatitis C infection and lichen planus, but its strength depends on where you live. In countries with a high prevalence of hepatitis C — parts of southern Europe, the Middle East and Japan — testing patients with lichen planus is standard. In Denmark, where prevalence is around 0.2–0.4%, routine screening is not usual practice; it is reserved for people with risk factors or with widespread or oral disease.

Stress

Stress can worsen existing lichen planus and in some cases trigger the first outbreak. Stress management is therefore part of treatment.

Who gets lichen planus?

Lichen planus on the skin affects around 0.2–1% of adults. Oral lichen planus is more common — around 1–2% — and is the form dentists most often encounter.

• Age: The condition occurs most frequently in adults between 30 and 60 years old and is rare in children.
• Sex: Women are affected slightly more often than men, especially by oral lichen planus.
• Genetics: A family history of lichen planus or other autoimmune diseases increases the risk.
• Other conditions: People with hepatitis C, HIV or other autoimmune conditions have an elevated risk.

How is lichen planus diagnosed?

The diagnosis is usually confirmed with a skin biopsy, in which a small piece of skin is examined under the microscope. This is necessary because several other conditions look like lichen planus: lichenoid drug eruption, psoriasis, eczema, discoid lupus, secondary syphilis and graft-versus-host disease. They cannot be told apart from a photograph alone.

In oral lichen planus there is also a small risk that an area develops into oral cancer over many years. The risk is concentrated in the erosive, ulcerated and atrophic forms, and the practical consequence is regular review by a dentist or doctor, plus a biopsy of any ulcer that will not heal and of new white or red patches.

How is lichen planus treated?

There is no cure, but lichen planus can usually be brought under control. Treatment depends on the severity and on which part of the body is affected:

Frequently asked questions