What is psoriasis?

Psoriasis is a skin condition that can cause sufferers much distress as a result of its unsightly appearance. It is thought to affect around 1-5 per cent of the population worldwide and has a tendency to run in families. The condition is less common in sunny climates and in pigmented skins. It can appear at any time but often develops in the teens or 20s or later in life, in the 50s and 60s.

Psoriasis can affect various areas of the body but in around 50 per cent of people it affects the scalp. The condition is unpredictable and symptoms may occur at irregular intervals. However, most people have mild, persistent symptoms for much of the time. Psoriasis is not infectious.

What are the symptoms of psoriasis?

In people with psoriasis, cells in the outer layer of the skin (the epidermis) are replaced at a faster rate than normal and there is inflammation in the epidermis and the layer of skin below (the dermis). This results in patches of psoriasis that often stand out from the skin - these raised patches are referred to as plaques. Plaques are often red and can be rounded in appearance. The surface of the affected skin is rough and scaly and can look silvery or shiny. Although the skin cells in these patches grow at a quicker rate than in normal skin this rapid growth is thought to be a symptom of psoriasis rather than a cause. Psoriasis does not cause ill health in any other way and many sufferers are generally very healthy. In some cases, psoriasis plaques may not cause the sufferer any problems while in others they may cause mild itching. It is not usually painful and the main complaint is of its appearance.

Plaque psoriasis (psoriasis vulgaris) is the most common type of psoriasis. The parts of the body most commonly affected are the knees, lower back, elbows, shoulders and scalp. The face, hands and feet are rarely affected.

Less common forms of the disease include guttate psoriasis (small spots), generalised psoriasis (all over the body), psoriasis of the nails, or pustular psoriasis.

What causes psoriasis?

Psoriasis is often an inherited condition but can also occur in people with no family history of the disease. If a parent has the condition it may be passed on to a child but this is not necessarily the case. For this reason, psoriasis is not considered to be a genetically inherited condition. Currently, there is no definite explanation for what causes psoriasis although it has been suggested that there are certain triggers that may cause it to develop, including injury, sunburn, HIV, β-haemolytic streptococcal infection, emotional stress, alcohol and certain drugs. It is not an infectious condition but, occasionally, the skin may become infected and need treatment.

There does not appear to be any connection between diet and psoriasis.

What treatment is available?

Natural sunlight seems to be of benefit in many psoriasis sufferers. However, the greater the exposure to sun, the greater the risk of developing skin cancer, so the amount of exposure to sunlight needs to be monitored carefully such that the risks do not outweigh the benefits. Sun lamps also have the potential to be harmful to skin and should only be used on the advice of your doctor.

Professional treatment may be available in the form of PUVA. This treatment involves the administration of a compound known as a psoralen (either orally [by mouth] or topically [applied to the skin]) followed two hours later by exposure to long-wave ultraviolet light (UVA) for 15 to 30 minutes. This treatment is repeated two or three times a week and in most people the psoriasis is cleared in four to six weeks. Although this treatment has been popular in the past, there are still risks associated with the future development of skin cancer and its use needs to be carefully supervised.

There are many topical products available for treating psoriasis:

Dithranol is available as a cream and is sometimes presented in combination with another medication such as salicylic acid. Dithranol is available in several different strengths ranging from 0.1 per cent to 3 per cent. Dithranol can irritate the skin. Its irritant potential is directly related to the strength being used, the time of contact and the patient's individual tolerance. Treatment is usually started using a short contact time (5-15 minutes) for at least one week. The contact time can then be increased stepwise to 30-60 minutes. The optimal period of contact will vary according to the patient's response to treatment.

The healthy skin surrounding the lesion to be treated can be protected by covering with a barrier agent (eg, Vaseline®) before applying the dithranol. At the end of each treatment period the skin should be rinsed thoroughly with cool to luke warm water before washing with soap. Dithranol may stain clothing and bedclothes.

Tar products such as coal tar may be used on areas where dithranol is unsuitable as they tend to be less irritant. Although the smell, colour and staining properties of coal tar make it undesirable, it does not have any significant side effects and the effects are usually long-lasting.

Cade oil may be used to treat psoriasis of the scalp. Cade oil is available only in combination with other substances such as coal tar.

Topical corticosteroids (eg, creams, gels and ointments) are useful for treating small areas of psoriasis but long-term use, particularly in large doses, is not advisable because of the potential side effects. Topical corticosteroids are often prescribed as the first treatment because they are so easy to use. Once-daily application is usually sufficient. Examples of topical steroids include beclometasone, betamethasone, clobetasol propionate, hydrocortisone and mometasone.

Vitamin D analogues such as calcipotriol (eg, Dovonex®), calcitriol (Silkis®) or tacalcitol (Curatoderm®) prevent the increased growth of skin cells seen in psoriasis plaques. The advantages of these products are that they do not smell and do not stain clothing. Dovobet® and Enstilar® are products that combine calcipotriol and the corticosteroid betamethasone. Dovobet is available as an ointment or gel and Enstilar comes as a foam; both can be used to treat psoriasis for up to four weeks.

Tazarotene (Zorac®) is a topical retinoid used in the treatment of mild to moderate psoriasis. The gel is applied once daily and can be used to treat up to 10 per cent of total body surface area. 

If topical treatments are not effective, systemic treatments may be tried. These are medicines that affect the whole body.

Acitretin (eg, Neotigason®) is a retinoid that may be given in severe psoriasis. The drug may harm an unborn child and pregnancy must therefore be avoided during treatment and for two years after treatment has stopped. 

Ciclosporin may be prescribed for severe psoriasis when other treatments have not worked. It is only used under strict medical supervision.

Methotrexate is another powerful drug and is usually given as tablets. As it can have other potentially serious effects on bone marrow its use must be carefully monitored and it will only be given in severe cases.

Adalimumab (Humira®), etanercept (Benepali®, Enbrel®), infliximab (Flixabi®, Inflectra®, Remicade®, Remsima®) and ustekinumab (Stelara®) are relatively new drugs administered by injection that can be used for moderate to severe chronic plaque psoriasis in patients who have failed to respond to, or who are intolerant of, or cannot take other systemic treatments, including ciclosporin, methotrexate and PUVA.

Secukinumab (Cosentyx®) and ixekizumab (Taltz®) are another type of new drugs that are given by injection. They can be used in patients with moderate to severe chronic plaque psoriasis even if they haven't tried other systemic treatments.

Apremilast (Otezla®) is another type of drug that can be given to patients who are unsuitable for other systemic treatments. It comes as tablets. 

Further information available from:

The Psoriasis Association
Dick Coles House
2 Queensbridge
Northampton NN4 7BF
Tel: 08456 760076

Psoriasis and Psoriatic Arthritis Alliance (PAPAA)
PO Box 111
St Albans
Herts AL2 3JQ
Tel: 01923 672837

Fact sheet provided by MIMS

Date last reviewed: May 2014

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