Psoriasis is a chronic, recurrent, noninfectious skin disorder that is characterized by red, scaly patches with fine silvery white scales when scratched. The lesions may appear anywhere on the body, but most commonly occur on the elbows, knees and scalp. The actual cause is unknown, but some evidence suggests psoriasis may be autoimmune. It is exacerbate by a few factors such as sunlight, stress, and illness. Treatment is tailored according to the type, severity and location of the psoriasis.