Psoriasis Psoriasis is one of the most important skin disorders because of its frequency, persistence and recurrent nature and tendency to disabled in a proportion of those it affects. It affects 1 to 2% of world population. The clinical features combined with some understanding of the genetic background and cascade of events involved in the production of skin lesion have served to focus the attention of researcher on to this disorder. One issue that has not yet been answered satisfactorily in whether psoriasis is one disease or several. Certainly there are several variance that differ. Sufficiently to question as to whether they represent separate disease or not. Psoriasis like (Psoriasiform) tissue reactions also occurs as a reaction to a range of stimuli, suggesting that the tissue alterations in psoriasis may only represents one important type of tissue response to injury. Psoriasis can start at almost any age and involves both the sexes equally. Most patients are worse in winter. It manifests in a variety of forms. Psoriatic arthritis develops in roughly one million people, 5 to 10% experience some disability, Psoriatic arthritis usually first appears between 30 and 50 yrs of age. Often months to years, after skin lesion first occurs.