Psoriasis is a chronic, non-contagious autoimmune disease that
affects the skin and joints. It commonly causes red, scaly
patches to appear on the skin. The scaly patches caused by
psoriasis, called psoriatic plaques, are areas of inflammation
and excessive skin production. Skin rapidly accumulates at these
sites and takes on a silvery-white appearance. Plaques
frequently occur on the skin of the elbows and knees, but can
affect any area including the scalp and genitals. In contrast to
eczema, psoriasis is more likely to be found on the extensor
aspect of the joint. The disorder is a chronic recurring
condition that varies in severity from minor localized patches
to complete body coverage. Fingernails and toenails are
frequently affected (psoriatic nail dystrophy) and can be seen
as an isolated finding. Psoriasis can also cause inflammation of
the joints, which is known as psoriatic arthritis. Ten to
fifteen percent of people with psoriasis have psoriatic
arthritis. The cause of psoriasis is not known, but it