What is psoriasis?

Psoriasis is a common skin disorder that affects men and women at any age.

It causes a thick, rough, dry build-up of the outer layer of the skin. These red patches on the skin are covered by silvery white scales and mainly develop on the knees, elbows, back or scalp, but almost any area of the body can be affected.

Psoriasis is not infectious and does not scar the skin.

Psoriasis is a chronic disease, which means you may have it for months or years. However early treatment may minimise the severity of the disorder.

What causes psoriasis?

Psoriasis is the growth of too many skin cells — a normal skin cell matures in 28—30 days but a psoriatic skin cell takes only 3—6 days. The exact cause of this is not known. There may be a genetic link that is triggered by another factor — for example, a throat infection, stress or injury to the skin.

There are certain times in life when the tendency to develop psoriasis is increased — for example, during puberty or in women during or after the menopause. However no obvious cause can be detected in the majority of people who develop psoriasis.

Are there different types of psoriasis?

There are different types of psoriasis, but it is important to remember that psoriasis changes over time — it may flare up, improve, change to another form, or several forms may exist at the same time:

  • Plaque psoriasis: This is the most common type of psoriasis. Raised, inflamed (red) lesions are covered with a silvery white scale. This scale is a build-up of dead skin cells. Plaque psoriasis may appear on any part of the skin, although it appears most commonly on the knees, elbows, scalp and trunk.
  • Guttate psoriasis: In guttate psoriasis small red dots of psoriasis develop most often on the trunk, arms and legs. There may be some scaling. Guttate psoriasis can be triggered by a throat infection, tonsillitis, a cold, chicken pox, immunisations, physical trauma, psychological stress, illness, or the administration of antimalaria drugs.
  • Flexural psoriasis: Red, shiny areas develop in the armpit, groin, under the breast and in other skin folds. Flexural psoriasis appears as smooth inflamed lesions without scaling and is prone to irritation due to rubbing and sweating.
  • Pustular psoriasis: Smaller, circular patches, filled with pus appear on the palms of the hands and soles of the feet. The pus is made up of white blood cells in the skin. It is not an infection and is not contagious.
  • Erythrodermic psoriasis: This is a serious but rare, complication of psoriasis. Large areas of the skin become hot, red and dry and you may also experience itching, pain and swelling. This is one of the few emergencies involving skin conditions. If you suffer from this disorder your doctor will admit you to hospital.
  • Psoriatic arthritis: About 10 percent of the people who have psoriasis will develop a form of arthritis called psoriatic arthritis. This causes inflammation and swelling in the hands, feet or in larger joints such as the knees, hips, elbows and the spine. It may cause stiffness, pain and joint damage.
  • Scalp psoriasis: Scalp psoriasis affects at least half of all people who have psoriasis. Raised, inflamed lesions covered with silvery white scales will develop on the scalp and particularly along the hair margins.
  • Nail psoriasis: Psoriasis can affect toenails and fingernails. It usually appears as pits in the nails and the nails may change to a yellowish colour and become thick or crumble easily. They may also be surrounded by inflammation. In some cases the nail may break away from the nail bed.

How is psoriasis diagnosed?

Your doctor will usually make the diagnosis by examining your skin and/or nails. Blood tests may be ordered if you also have inflamed joints.

How is psoriasis treated?

Although there is no cure for psoriasis, treatment is usually effective. The skin becomes less scaly and may look completely normal. However there is a tendency for psoriasis to return. There are several different treatments available and you should discuss with your doctor which treatments are best suited to you:

  • Moisturising creams and ointments — these will moisturise dry skin and are a substitute for soap when washing the skin.
  • Bath oils — some of these contain tar or antiseptics, which can provide other benefits in addition to the moisturising effect.
  • Regular daily doses of sunlight taken in short exposures can help to improve psoriasis. Sunburn may make psoriasis worse.
  • Tar creams, ointments, lotions and shampoos help to reduce scaling and have an anti-inflammatory effect.
  • Vitamin D-based topical (applied to the skin) preparations can be effective.
  • Salicylic acid-based applications can help to remove thick layers of overgrown skin and scales.
  • Stronger medications can be prescribed by a dermatologist and can be very helpful if used appropriately.
  • Mild steroid creams and ointments can be used for short periods to treat psoriasis on the face or in body folds.

What can I do?

Because the cause is not yet known, doctors do not know how to prevent psoriasis. However you may be able to prevent serious outbreaks by treating small plaques when you first see them and it does help to use skin moisturisers instead of soap to prevent the skin from drying.

My psoriasis is very bad and isn’t responding to treatment. Are there any other options?

There are other options for people with severe psoriasis (i.e. at least 20% of their body surface is covered with psoriasis) who do not respond to the treatments listed above. These treatments are effective but are used only under strict supervision and only after the other, simpler treatments have been tried first.

There are side-effects to all of these treatments which your doctor will discuss with you. You must also advise your doctor if you are pregnant, as many of these treatments cannot be used during pregnancy:

  • Photochemotherapy (PUVA) — PUVA is a term used for a combined treatment with psoralen, a light-sensitive drug and ultraviolet A light.
  • Retinoids — drugs derived from Vitamin A) with or without PUVA.
  • Hydroxyurea — drugs that slow down the rapidly dividing skin cells.
  • Cyclosporin A — drugs that suppress the immune system.

What is psoriatic arthropathy?

Psoriatic arthropathy is a form of arthritis that affects about 10—20% of people with psoriasis.

The arthritis affects the lining of joints causing swelling, pain and stiffness.

The arthritis is usually limited to just a few joints and sometimes affects the spine, giving a painfully stiff back or neck. It can also affect other joints such as the knees.

Frequently finger and toe-nails develop pits, discoloration and thickening. The outlook is generally good, as psoriatic arthritis is not usually a crippling disease.

See Psoriasis Clinic

Back to top of page

Reviewed: December 7, 2006