The symptoms of psoriasis (suh-RYE-uh-sihs), like scaling, itching, and redness, are due mainly to the over-production of cells in the skin's outer layer. While a normal skin cell may take a month to mature and be replaced, in a person with psoriasis, skin cells mature in just three to six days. Thus, dead skin builds up faster than it can be shed. Doctors still aren't sure what causes this disorder. However, new studies suggest that psoriasis is an autoimmune disorder in which the body attacks itself. One of the defenders in your immune system is the T cell, a type of white blood cell that normally fights off disease and infection. In psoriasis patients, it's believed that the immune system mistakenly releases T cells as if an injury or infection were present. This release of T cells speeds up skin cell production, increases blood flow to the area, and creates inflammation. Over time, psoriasis may go through periods of worsening, then improving. It's thought that such flare-ups, or perhaps the condition itself, may be triggered by factors like climatic changes, stress, infections, and certain medications, such as beta-blockers, anti-depressants, and steroids. In addition, about one-third of patients may inherit a tendency toward psoriasis.