Epidemiology of psoriasis: clinical issues.

Psoriasis is a genetically inherited spectrum of skin diseases characterized by epidermal proliferation and inflammation, which are reversible. Although many have reported that psoriasis is triggered by trauma, infections, stress, drugs, etc., the epidemiology of psoriasis remains poorly understood. Linkage to human leukocyte antigen-(HLA)-Cw6 and DR7 is strong in people with early onset disease, but concordance in monozygotic twins is only 67%, emphasizing the importance of a triggering event. Other factors that have been reported to affect the course of psoriasis include upper respiratory infections, smoking, obesity, alcohol ingestion, regional enteritis, and human immunodeficiency virus infection. This manuscript reviews the clinical epidemiology of psoriasis and highlights some of the needs for further investigation into specific areas of the disease.