In psoriasis, the turnover of the skin is increased. New cells are made too quickly and push up to the surface of the skin while all the previous layers haven't yet been shed. This leads to raised red patches and scales.

No one knows exactly what causes psoriasis. So many treatments have developed through simply observing what helps the condition.

Sunlight

Regular doses of sunlight (which contains ultraviolet light) can improve psoriasis, although for a few people it makes it worse and strong sunlight should be avoided.

Ultraviolet light treatment may be used for certain types of psoriasis, particularly chronic plaque and guttate psoriasis. This treatment is usually given in hospital. Special creams and ointments are first applied to the areas affected by psoriasis, and the combination of light and medication may be very effective.

PUVA

There's a special type of ultraviolet light treatment called PUVA, which is often used in psoriasis. PUVA is used for particularly severe cases of psoriasis that can't be controlled by topical treatments alone.

It's called PUVA because it involves using a type of chemical called psoralens (which are found in some plants), in combination with ultraviolet A light. Ultraviolet A, or UVA, is a particular wavelength of ultraviolet light which doesn't tend to cause burning, although it can age the skin. The psoralens make the skin respond better to the UVA treatment.

How PUVA is given

The psoralen drug is taken a couple of hours before the light treatment to allow it to be absorbed by the body and the skin. Sometimes you're simply asked to sit soaking in a bath of psoralen solution for ten minutes before the light treatment. This is a different way to get the chemical into the skin.

Then you'll stand or lie surrounded by long fluorescent tubes which give off the UVA light (like in a sunbed). You must wear eye patches because there's a risk of cataracts if your eyes are exposed to the light.

You'll probably have a few treatments each week until the skin starts to improve. This will then be reduced to weekly or fortnightly maintenance therapy for as long as is necessary.

Great care has to be taken in its use because there's a slight risk of skin cancers developing, and if you have too much PUVA, the skin can age prematurely. So the treatment is given in hospital and closely supervised.

You can find out more from:

The Psoriasis Association
Milton House, 7 Milton Street, Northampton NN2 7JG
Tel: 01604 711129
Fax: 01604 792894
Website: www.psoriasis-association.org.uk

This article was last medically reviewed by Dr Trisha Macnair in June 2008