Psoriasis is a common, chronic relapsing/remitting immune-mediated skin disease characterized by red, scaly patches, papules, and plaques, which usually itch. The skin lesions seen in psoriasis may vary in severity from minor localized patches to complete body coverage. The disease affects 2–4% of the general population.
The causes of psoriasis are not fully understood. Psoriasis is not purely a skin disorder and can have a negative impact on many organ systems. Psoriasis has been associated with an increased risk of certain cancers, cardiovascular disease and other immune-mediated disorders such as Crohn's disease andulcerative colitis. It is generally considered a genetic disease thought to be triggered or influenced by environmental factors. Psoriasis develops when the immune system mistakes a normal skin cell for a pathogen, and sends out faulty signals that cause overproduction of new skin cells.