Normally, skin cells are constantly being formed deep beneath the surface of your skin. Over about a month, these cells are pushed up to the surface. This is called cell turnover. The cells eventually die and flake off, revealing new skin cells.

In people with psoriasis, the skin cells grow too quickly. The exact cause of psoriasis is not completely understood, but genetic and immune system abnormalities are believed to play key roles in the condition. In psoriasis, cell turnover can happen in a matter of days. A faulty immune system signals increased growth cycle of skin cells. Layers of skin build up, forming a whitish, flaky crust. Blood vessels increase flow in an attempt to nourish this skin, which leads to redness and swelling. The classic symptoms of psoriasis are reddened, inflamed skin with a whitish, flaky layer of dead cells on top.

Although psoriasis usually appears as a skin condition, recent discoveries show that its real cause is a problem with the immune system.

Your body naturally fights infections and heals injuries with special cells -- called white blood cells -- that battle viruses or bacteria. Normally, these cells go to the site of infection or injury to help repair wounds and prevent infection. One byproduct of this normal process is inflammation (redness and swelling).

For reasons that doctors don't yet understand, the immune systems of people with psoriasis malfunction. One type of white blood cell, the B-cell, begins creating antibodies that destroy normal skin cells. Another type of white blood cell, the T-cell, begins overproducing a type of protein called a cytokine. This overproduction appears to turn off a signal that controls the growth of skin cells.

So this is why psoriasis is considered an autoimmune disease -- your own immune system malfunctions and attacks normal body tissues. Other autoimmune diseases include lupus and rheumatoid arthritis.