Knees, elbows, trunk and scalp are the most common locations. Patches on your scalp can shed large quantities of silvery-white scales resembling severe dandruff. In more severe cases, pustules, cracked skin, itching, minor bleeding or aching joints also may develop. In addition, your fingernails and toenails may lose their normal luster and develop pits or ridges. These skin eruptions are due to overly rapid growth of cells in your skin's outer layer.
Many people also inherit a tendency toward psoriasis.
Dry skin, skin injuries, infections, certain drugs, obesity, stress and lack of sunlight can all aggravate your symptoms. Psoriasis isn't contagious. You can't spread it to other parts of your own body, or to other people, simply by touching. Psoriasis typically goes through cycles. The symptoms can persist for weeks or months, followed by a break.