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What is psoriasis?

psoriasisPsoriasis is a common skin problem affecting about 2% of the population. It occurs equally in men and women, at any age, and tends to come and go unpredictably. It is not infectious, and does not scar the skin.

What causes psoriasis?

The skin is a complex organ made up of several different layers. The outer layer of skin (the epidermis) contains cells which are formed at the bottom and then move up towards the surface, gradually changing as they go, finally dying before they are shed from the surface. This journey normally takes between 3 and 4 weeks. In psoriasis, the rate of turnover is dramatically increased within the affected skin, so that cells are formed and shed in as little as 3 or 4 days. The reasons for this are still not fully understood.

Some people are more likely to develop psoriasis than others, particularly if there is someone else in their family who has psoriasis: in other words, it is a genetic or hereditary disease (see below). However, the trigger for psoriasis to appear is often an outside event, such as a throat infection, stress or an injury to the skin.

In practice, for most patients who develop psoriasis, or for whom it clears and then comes back, no obvious cause can be detected. Usually, sunlight improves psoriasis, though occasionally it makes it worse (especially if the skin gets burned). A high alcohol intake and smoking can worsen psoriasis too, as can medicines used for other conditions - such as lithium, some tablets used to treat malaria, and other drugs such as beta blockers (medicines commonly used to treat angina and high blood pressure). There is no apparent relationship between diet and psoriasis.

Is psoriasis hereditary?

Yes, but the way it is inherited is complex and not yet fully understood. Many genes are involved, and even if the right combination of genes has been inherited psoriasis may not appear.

Other features of the inheritance of psoriasis are:

What are the symptoms of psoriasis?

The main problem with psoriasis for many people lies in the way it looks, and the way it attracts comments from others. This can affect their quality of life. Psoriasis can itch and the affected skin can split, which may be painful. Some people with psoriasis may develop stiff and painful joints, which can be due to a form of arthritis associated with psoriasis called psoriatic arthropathy. The joints most commonly affected are those at the ends of the fingers and toes.

What does psoriasis look like?

Lesions of psoriasis (often known as plaques) are pink or red, but covered with silvery-white scales. They can form a variety of shapes and sizes, and have well-defined boundaries with the surrounding skin. Some arise where the skin has been damaged, for instance by a cut or a scratch: this is known as the Köbner phenomenon. On the scalp, the scales heap up so that the underlying redness is hard to see. In contrast, in body folds such as the armpits and groin, the red well-defined areas are easy to see but are seldom scaly.

The severity of psoriasis varies with time, and from person to person. When it is mild, there may be only one or two plaques: when it is more severe there may be large numbers. The plaques can take up a variety of patterns on the skin:

Changes in the nails can often be seen too, if looked for carefully. They appear in up to a half of people with psoriasis. The most striking ones are:

How will psoriasis be diagnosed?

Can psoriasis be cured?

No. However, treatment to control the signs and symptoms is usually effective. The skin becomes less scaly and may then look completely normal. However, even if your psoriasis disappears after treatment, there is a tendency for it to return. This may not happen for many years, but can do so within a few weeks.

How can psoriasis be treated?

This will depend on the type of psoriasis that you have, and on its severity.

1. Topical therapies

Topical treatments for special sites

2. Phototherapy
This term refers to treatment with various forms of ultraviolet light, sometimes assisted by taking particular tablets. It is helpful if the psoriasis is extensive, or fails to clear with topical treatment, or comes back quickly after seeming to clear. Topical therapy will usually continue during the phototherapy. Two types of ultraviolet (UV) light may be given, using special machines: UVA and UVB. These are different parts of normal sunlight. Treatment with UVA is helped by taking a medication known as a psoralen — a combination known as PUVA therapy. Treatment with UVB does not need tablets.

Both UVB and PUVA treatments have to be given with great care, and you will have to come up to the skin department 2 or 3 times a week for a number of weeks. Full details are given in other leaflets issued by the British Association of Dermatologists ('Treatments for moderate or severe psoriasis' and 'Phototherapy').

3. Internal treatments
The idea of using a tablet to treat psoriasis is attractive, but the effective ones all have potential risks, so they are not used for psoriasis if it can be kept under control in simpler ways. In addition, you will usually have to continue with some topical therapy even though you are taking the tablets.

Your dermatologist will discuss the risks with you if you start on this kind of treatment. All of the tablets will require blood tests, and many interfere with other medicines. Female patients should not become pregnant whilst on any tablets for psoriasis, and with some of them it is important that male patients should not father a child.

The tablets in question include acitretin (related to vitamin A), ciclosporin (suppresses the immune system), methotrexate (slows down the rate at which the skin cells are dividing in psoriasis), and hydroxycarbamide (formerly known as hydroxyurea - also slows down the rate at which the skin cells are dividing). There are also several injectable forms of treatment available for extremely severe forms of psoriasis (etanercept, infliximab, adalimumab,ustekinumab).

What can I do?