is a common autoimmune disease of the skin, affecting up to two percent of the U.S. population. It is characterized by chronic rashes that often fade and recur, and there are several different subtypes. The most common type is called plaque psoriasis, and this classically manifests as scaly red patches that often occur on the extensor surface of joints (i.e. the backs of the elbows and fronts of the knees). However, the rash can occur anywhere on the body, and is often found on the scalp, buttocks, and back. Often times, the skin on these patches builds up and thickens, giving it a distinctive silvery/white appearance. Other symptoms can include pitting of the fingernails and toenails, as well as inflammation of the joints (classically involving swelling of the fingers and toes).
Topical creams and ointments are the mainstay of treatment for psoriasis, including moisturizers, coal tar, and corticosteroids. For more advanced disease, repeated sessions of phototherapy (exposure to ultraviolet light) may be used. Treatment of advanced skin disease or psoriatic arthritis
may also involve systemic oral, subcutaneous or intravenous medications which work by suppressing the body' immune system.