Psoriasis is fairly common skin disorder that may affect people of any age, though it usually begins between ages 15 and 35. It can appear both suddenly or slowly, and in many cases, it goes away only to repeatedly flare up again as a lifelong condition. Little is known about what causes psoriasis. In psoriasis there is an overproduction of skin cells which rise too quickly to the outer layer and build up as dead cells on the skin's surface. An outbreak of psoriasis may be your body’s response to other illnesses such as a bacterial or viral infection, or environmental triggers such as dry air. Skin injuries, sun overexposure, even stress can all contribute. Symptoms can include not only irritated, itchy patches of skin, but also redness and discoloration, dry and flakey scaling, and additionally joint pain, and changes to nails. Psoriasis can appear anywhere on the body, but it is most often seen on elbows, knees and scalp. Though it is not contagious, it is thought to be an inherited disorder.