Psoriasis is a chronic, recurring disease that causes one or more raised, red patches that have silvery scales and a distinct border between the patch and normal skin.
A problem with the immune system may play a role, and some people are genetically predisposed to psoriasis.
Characteristic scales or red patches can appear anywhere on the body in large or small patches, particularly the elbows, knees, and scalp.
This disease is treated with a combination of exposure to ultraviolet light (phototherapy), drugs applied to the skin, and drugs taken by mouth or given by injection.
Psoriasis is common and affects about 1 to 5% of the population worldwide. Light-skinned people are at greater risk, whereas blacks are less likely to get the disease. Psoriasis begins most often in people aged 16 to 22 years and aged 57 to 60 years. However, people in all age groups and races are susceptible.
The patches of psoriasis occur because of an abnormally high rate of growth of skin cells. The reason for the rapid cell growth is unknown, but a problem with the immune system is thought to play a role. The disorder often runs in families, and certain genes are associated with psoriasis.