Patches of red, thickened, scaly skin, often affecting many areas of the body

  • Often runs in families
  • May be aggravated by stress
  • Age as a risk factor depends on the type
  • Gender is not a significant factor

Psoriasis is common in Western countries, Australia and South America, and parts of Asia and Africa: it affects about 2 per cent of the UK population. There are several different types, most of which are difficult to control and flare up throughout life. Red, thickened, scaly skin occurs in all types of psoriasis. The scaly areas do not always itch, but if the condition affects many parts of the body, psoriasis may cause severe physical discomfort as well as embarrassment in public.

In areas of skin that are affected by psoriasis, new skin cells are produced at a much faster rate than dead cells are shed and the excess skin cells accumulate to form thick patches. The cause is not known, but an episode of psoriasis may be triggered or aggravated by infection, injury, or stress. The disorder often runs in families, which suggests that a genetic factor may be involved; approximately 1 in 3 people with psoriasis has a close relative who also has the condition. The use of certain drugs, such as antidepressants, antihypertensives, beta-blockers, and antimalarial drugs, can produce psoriasis in some people.

What are the types?

There are four main types of psoriasis, each of which has a distinctive appearance. Some people may be affected by more than one type of the disorder.

Plaque psoriasis

The most common form of psoriasis, plaque psoriasis is a lifelong disorder that may develop in people of any age. The condition may produce the following symptoms:

  • Patches called plaques, consisting of thickened, red skin and scaly surfaces. They usually occur on the elbows, knees, lower back, and scalp; behind the ears; and at the hairline. In some cases, they develop on old scar tissue.

  • Intermittent itching of affected areas.

  • Discoloured nails that are covered with small pits. In severe cases, the nails lift away from the nail beds. Sometimes the nails may become thickened and the condition may be mistaken for a fungal infection.

The symptoms of plaque psoriasis tend to continue for weeks or months and may recur intermittently.

Plaque psoriasis on the elbow

The elbows are a common site for plaque psoriasis. The scaly surfaces of the patches are accumulations of dead skin cells.

Guttate psoriasis

This form most commonly affects children and adolescents and often occurs after a bacterial throat infection. Typical symptoms are:

  • Numerous coin-shaped, pink patches of scaly skin, each about 1 cm ( 3 / 8 in) across, mainly on the back and chest.

  • Intermittent itching of the affected areas of skin.

These symptoms usually disappear in 4–6 months and do not recur, but more than half of those affected later develop another form of psoriasis.

Guttate psoriasis

The small, pink, scaly patches of guttate psoriasis are often spread over large areas. A typical site is the back, as shown here.

Pustular psoriasis

This is a rare but potentially life-threatening type of psoriasis that mainly affects adults. The condition may appear abruptly, with the following symptoms:

  • Small blisters filled with pus that develop on the palms of the hands and the soles of the feet.

  • Widespread areas of red, inflamed, and acutely tender skin.

  • Some thickening and scaling of the inflamed areas.

In severe cases, pustular psoriasis may affect the entire body and require hospital treatment.

Flexural psoriasis

Elderly people are commonly affected by this type of psoriasis, in which large, moist, red areas develop in skin folds rather than over widespread body areas. The rash often affects the groin, the skin under the breasts, and sometimes the armpits. Flexural psoriasis usually clears up with treatment but may recur.

Are there complications?

About 1 in 10 people with psoriasis of any type develops a form of arthritis that usually affects the fingers or knee joints. In pustular psoriasis, a massive loss of cells from the surface of the skin may lead to dehydration, kidney failure, infections, and high fever. If left untreated, the condition can be life-threatening.

What might be done?

Your doctor should be able to diagnose the type of psoriasis from its appearance. If you have only mild psoriasis that does not cause problems, you may decide not to treat the skin symptoms. Otherwise, you should follow the treatment that your doctor recommends.

Topical treatments

Psoriasis is commonly treated with emollients to soften the skin (see Emollients and barrier preparations). Other common treatments are preparations containing coal tar or a substance called dithranol, which reduce inflammation and scaling. Coal tar and dithranol are effective but coal tar smells unpleasant and both can stain clothing and bed linen. Dithranol should be applied to affected areas only because it can irritate healthy skin.

Alternatively, your doctor may prescribe a topical preparation containing either the vitamin D derivative calcipotriol (see Vitamins) alone or calcipotriol in combination with a topical corticosteroid. These preparations are usually applied once or twice a day, do not smell, and do not stain clothes or skin. Calcipotriol alone may take up to about 12 weeks to have maximum effect, whereas a combined calcipotriol and corticosteroid preparation often achieves faster results. However, it is important not to overuse these preparations and you should follow the advice of your doctor.

Topical corticosteroids alone may also be prescribed. However, the drugs should be used sparingly because they may cause long-term side-effects, such as thinning of the skin.

Generalized treatments

For widespread psoriasis that does not respond to topical treatments, therapeutic exposure to ultraviolet (UV) light is often effective. UV therapy is usually given without oral medications. PUVA therapy involves using UV therapy together with psoralen, an oral drug that is taken before the ultraviolet light treatment and helps to make the skin more sensitive to the effects of light. This combined treatment slightly increases the risk of skin cancer and is given only under the supervision of a dermatologist.

Regular, short doses of sunlight often help to clear up psoriasis. Moderate exposure of affected areas to sunlight, if the weather is sufficiently warm, can be beneficial, but you should adopt sensible precautions to avoid sunburn (see Safety in the sun).

In some severe cases of psoriasis, for which topical preparations may not be effective, treatment with oral or intravenous drugs may be recommended. The drugs used for this treatment include retinoids, methotrexate (see Anticancer drugs), and ciclosporin (see Immunosuppressants). However, retinoid drugs and methotrexate can all cause abnormalities in a developing fetus. For this reason, you should not take any of these drugs if you are pregnant or planning to have a child.

What is the prognosis?

Although there is no cure for psoriasis, treatment can relieve the symptoms and help many people with the condition to lead a normal life. If psoriasis is a long-term problem, you may find it beneficial to join a self-help group.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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