What it is

Lichen planus is a skin condition that causes violet or skin-coloured itchy rashes. It can occur anywhere on the body — the limbs, trunk, scalp, genitals and mouth — and it sometimes involves the nails. On the skin it usually appears as purple-pink bumps with white streaks on the surface. The itch can be very severe. Wider and thicker patches sometimes appear on the lower legs, and very rarely there are blisters. It often starts around the wrists or ankles and can spread from there.

In the mouth it appears as a whitish lacy pattern on the lining, with a burning feeling, especially with spicy food. The nails may become thin and split lengthways. When the scalp is involved there may be loss of hair.

What causes it

The exact cause is not known. It can sometimes be related to an allergic or immune response to medicines — antibiotics, antimalarials, diuretics and others — or to hepatitis C infection. Stress is often a triggering or aggravating factor. Lichen planus does not spread from person to person, and it is not hereditary.

How we treat it

Lichen planus may last a few months to two years, during which time it usually settles. Sometimes it comes and goes over several years. While it is present it can be extremely troublesome, so treatment is worthwhile.

Emollients and antihistamines are given in daily doses to relieve the itch. Topical steroids, sometimes under an occlusive dressing, and oral steroids are used to flatten the lesions and suppress the immune response. Steroids may be injected directly into very thick lesions. In severe generalised lichen planus, acitretin — a drug derived from vitamin A — may lead to faster healing. Lesions in the mouth need careful monitoring until they settle, and nail lesions are quite resistant to treatment. When the rash clears it leaves dark-coloured marks, which may last several years.