Psoriasis is not seen in small children; in fact it has almost nil cases in India. It is hard to judge when does it starts. Mostly it has been noticed that psoriasis catches adults. The reason behind this disease is the unhealthy diet of our skin. This is the worst ailment in the category of skin disorder. This disease causes itchy rashes and makes our skin black. The itchiness irritates the patient so much that if he scratches the affected area it emits a sort of liquid which spoils the clean area as well. To treat this you should take proper medical treatment and believe that it is curable.