| Summary: | Psoriasis is a common skin disorder characterized by focal formation of raised plaques that constantly shed scales derived from excessive growth of skin epithelial cells. The disease is characterized by a series of linked cellular changes in the skin: hyperplasia of epidermal keratinocytes, vascular hyperplasia and ectasia, and infiltration of T lymphocytes, neutrophils, and other types of leukocyte in the affected skin. Psoriasis is now considered as a T cell-mediated inflammation of the skin. Types of psoriasis that may be clinically encountered include plaque psoriasis, guttate psoriasis, erythrodermic psoriasis, pustular psoriasis, nail psoriasis, psoriatic arthritis, and scalp psoriasis. Psoriasis is believed to be genetically linked but can also be triggered by mechanical, ultraviolet, and chemical injury; various infections; prescription drug use; psychological stress; smoking; and other factors.
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