Psoriasis (play /səˈraɪ.əsɨs/) is an autoimmune disease that affects the skin. It occurs when the immune system mistakes the skin cells as a pathogen, and sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious.[1] However, psoriasis has been linked to an increased risk of stroke,[2] and treating high blood lipid levels may lead to improvement.[3] There are five types of psoriasis: plaque, guttate, inverse, pustular, and erythrodermic. The most common form, plaque psoriasis, is commonly seen as red and white hues of scaly patches appearing on the top first layer of the epidermis (skin). Some patients, though, have no dermatological symptoms. The name psoriasis is from Ancient Greek, meaning roughly “itching condition” (psora “itch” + -sis “action, condition”).

In plaque psoriasis, skin rapidly accumulates at these sites, which gives it a silvery-white appearance. Plaques frequently occur on the skin of the elbows and knees, but can affect any area, including the scalp, palms of hands and soles of feet, and genitals. In contrast to eczema, psoriasis is more likely to be found on the outer side of the joint.