A team from Leicester University have uncovered detailed genetic differences in people who have the condition.

They believe their work could lead to new, more effectively targeted drugs.

Psoriasis, which occurs when the skin replaces itself too quickly, affects more than one million people in the UK. There are many different forms.

It usually appears as red, scaly patches that when scraped or scratched reveal fine silvery scales.

The patches may itch and feel uncomfortable. Some people develop a specific form of arthritis related to psoriasis.

Lead researcher Professor Richard Trembath said: "In individuals that are genetically predisposed to become affected, the disease can be triggered by a number of environmental agents, such as bacterial infections or stress.

"We have long been engaged in the search for genes that make people vulnerable to the action of psoriasis-triggering factors.

"Our past studies have demonstrated that a small region of what is known as Chromosome 6 contained at least one of such psoriasis susceptibility genes.

"A closer examination of this genetic interval identified a gene called CDSN, responsible for the adhesion and shedding of skin cells.

"We have now identified a CDSN DNA variant, which is significantly more frequent among psoriatic patients, compared to unaffected individuals.

"This variant may confer susceptibility to psoriasis by causing an accumulation of CDSN protein, which in turn could contribute to the inflammatory response observed in the skin of patients.

"This discovery represents a significant step towards the understanding of the molecular causes of psoriasis and the design of targeted therapeutic approaches."

Potentially significant

David Chandler, of the Psoriatic Arthropathy Alliance, said the research could be significant.

He said: "It is important to identify the cause of psoriasis, as many people with psoriasis still feel that it is something they have done wrong as opposed to just unlucky genes."

Mr Chandler said more targeted therapies would be a big step forward, as doctors often still had no idea of which patients would respond to treatment, and which would not.

Not only was this frustrating for patients, it also meant the NHS wasted money.

"As someone with psoriasis and psoriatic arthritis I would be very keen to know what triggers my disease and if these triggers could be identified.

"Many treatments are toxic or have side effects and if I knew they would work then maybe I would willing to put-up with side-effects."

Gladys Edwards, chief executive of the Psoriasis Association, said: "Psoriasis is a complex condition and for some people it may have a profound effect on daily life.

"The Psoriasis Association welcomes all advances which increase the knowledge and understanding of the fundamental causes of psoriasis.

"This in turn will hopefully lead to the development of improved treatments which are effective, safe and acceptable in the long term."

A recent survey of more than 5,000 European people found people with psoriasis are often treated as social outcasts.

Half of those questioned said they would not kiss, swim with or eat food prepared by someone with psoriasis.