Psoriasis cross section video clip. CGI representation of Psoriasis.  Psoriasis is a chronic skin condition that causes cells to build up rapidly on the surface of the skin. The extra skin cells form scales and red patches that are sometimes itchy and painful. The most common areas affected are the scalp, elbows, and knees, but it can appear anywhere on the body. The exact cause of psoriasis is not known, but it is thought to be related to an immune system problem. It is not contagious and can occur in people of all ages. Symptoms can range from mild to severe and may come and go. Treatment options include topical creams, light therapy, and oral or injectable medications. In some cases, lifestyle changes such as stress management and avoiding triggers can also help manage symptoms.