A person with psoriasis may have only a few lesions, or it can be widespread across most of the body. Researchers are not certain what causes the disease. It is believed to be an immune-mediated disease. Heredity seems to play a part, as do environmental factors. Scientists believe that a biochemical stimulus triggers the abnormally high skin cell growth.
Psoriasis affects females slightly more than males in all age groups.
While all races have the disease, Caucasians tend to have a slightly higher incidence. It appears most often between the ages of 15 and 35, though it can strike in infancy or old age. There is no specific medical test for psoriasis. A physician usually makes the diagnosis after examining the skin, scalp, nails and, sometimes a biopsy under a microscope. There are several forms of psoriasis.