Psoriasis is a common skin disorder affecting around 2% of people in the UK.

Different types of psoriasis cause different symptoms, The most common type, plaque psoriasis, causes thick red plaques covered with silvery scales.

Psoriasis image Interactive Medical Media, LLC

The most common areas affected are the scalp, elbows, knees, and lower back, although any skin surface may be involved. It can also occur in the nails and body folds.

Psoriasis is not contagious and cannot be passed from person to person, but it can occur in members of the same family.

Psoriasis usually begins in early adulthood or later in life. In most people, the rash is limited to a few patches of skin; in severe cases, it can cover large areas of the body. The rash can heal and come back again throughout a person's life.

Psoriasis starts as small red bumps, which enlarge and become scaly. The skin appears thick, but bleeds easily if the scales are picked or rubbed off.

In addition, the rash may produce:

If you have a rash that is not healing, seek medical advice for evaluation of the rash to determine if it is psoriasis.

The signs of psoriasis vary depending on the type you have. Some common signs for plaque psoriasis - the most common variety of the condition - include:

Psoriasis can also be associated with psoriatic arthritis, which causes pain and swelling in the joints. The Psoriasis Association estimates that between 5% and 7% of people with psoriasis have psoriatic arthritis, but this figure rises to about 40% in people who have severe psoriasis.

The exact cause of psoriasis is unknown, but it is believed that a combination of factors contributes to the development of the condition. An abnormality in the immune system causes inflammation in the skin, triggering new skin cells to develop too quickly. Normally, skin cells are replaced every 28 to 30 days. With psoriasis, new cells grow and move to the surface of the skin every three to four days. The build-up of old cells being replaced by new cells creates the silver scales of psoriasis.

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Psoriasis - WebMD Boots