Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including genetics. Common triggers include trauma, infection, and certain drugs. Symptoms are usually minimal, but mild to severe itching may occur. Cosmetic implications may be major. Some people develop severe disease with painful arthritis (psoriatic arthritis). Diagnosis is based on appearance and distribution of lesions. Treatment can include topical treatments (eg, emollients, vitamin D3 analogs, retinoids, coal tar, anthralin, corticosteroids), phototherapy, and, when severe, systemic drugs (eg, methotrexate, oral retinoids, cyclosporine, immunomodulatory agents [biologics]).