A skin condition causing scaling and inflammation. Psoriasis is caused by a defect in cell turnover, a process in which skin cells grow deep in the skin and slowly rise to the surface over the course of a month. In psoriasis, the immune system triggers abnormally fast cell turnover, creating patches of thick, red skin with silvery scales. These itchy, sore patches most often form at the elbows, knees, or scalp, but can also affect the face, fingernails, toenails, soft tissue of the genitals, or any skin-covered region of the body.

Some patients respond well to ointments or creams containing corticosteroids, vitamin D, or retinoids. Ultraviolet (UV) light, in the form of natural sunlight or artificial UV light administered by a doctor, may also help.

For more severe forms of psoriasis, several systemic medications can be administered by pill or injection. These include retinoids and the immunosuppressants cyclosporin and methotrexate. Since the mid-2000s, drugs called biologic response modifiers, proteins made by living cells, have become available. Taken by injection, they block specific immune system processes that cause inflammation and the overproduction of skin cells. These drugs include infliximab, etanercept, certolizumab, adalimumab, golimumab, ustekinumab, and secukinumab. In 2014, the U.S. Food and Drug Administration (FDA) approved apremilast for treating moderate-to-severe psoriasis. Apremilast, a new type of drug called a PDE4 inhibitor, is taken in pill form. Sometimes light therapy is combined with systemic therapy, allowing lower doses of each to be used.

Want to learn more about psoriasis and psoriatic arthritis? Read “Psoriatic Arthritis Symptoms, Treatments & Diagnosis” and “How Psoriasis Can Lead to Psoriatic Arthritis.”

Robert S. Dinsmoor is a medical writer and editor based in Massachusetts.

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