Psoriasis is a common skin disease.
Psoriasis involves hyperproliferation of the keratinocytes in the epidermis.
The cause of the loss of control of keratinocyte turnover is unknown. However, environmental, genetic, and immunologic factors appear to play a role. In some families, psoriasis is an autosomal dominant trait. The epidermis is infiltrated by a large number of activated T cells, which appear to be capable of inducing keratinocyte proliferation. Approximately 6.4 million Americans have psoriasis.