Psoriasis is an immune-mediated disease which affects the skin and joints. When it affects the skin it commonly appears as red scaly elevated patches called plaques. Psoriasis plaques frequently occur on the elbows and knees, but can affect any area of skin including the scalp and genital area. Psoriasis can vary in severity, from minor localized patches to extensive or even complete skin coverage. Fingernails and toenails are often affected (psoriatic nail dystrophy). Psoriasis can also cause inflammation of the joints. This is known as psoriatic arthritis. Who Gets Psoriasis? More than 4.5 million adults in the United States have been diagnosed with psoriasis, and approximately 150,000 new cases are diagnosed each year. An estimated 20% have moderate to severe psoriasis. Is Psoriasis Gender Biased? Psoriasis occurs about equally in males and females. Recent studies show that there may be an ethnic link. It seems that psoriasis is most common in Caucasians and slightly less common in African Americans. Worldwide, psoriasis is most common in Scandinavia and other parts of northern Europe. It appears to be far less common among Asians and is rare in Native Americans. There also is a genetic component associated with psoriasis. Approximately one-third of people who develop psoriasis have at least one family member with the condition. Research shows that the signs and symptoms of psoriasis usually appear between 15 and 35 years of age. About 75% develop psoriasis before age 40. However, it is possible to develop psoriasis at any age. After age 40, a peak onset period occurs between 50 and 60 years of age. Childhood Psoriasis About 1 in 10 people develop psoriasis during childhood, and psoriasis can begin in infancy. The earlier the psoriasis appears, the more likely it is to be widespread and recurrent. There is growing emphasis on quality of life research in all of medicine, and psoriasis impacts on every dimension of health-related quality of life. In my patient population, many of my patients are spending an hour a day taking care of their psoriasis and are using numerous treatments. Psoriasis treatment is costly, financially and psycologically. Psoriatic Arthritis Psoriatic arthritis develops in roughly one million people across the United States, and 5% to 10% experience some disability. Psoriatic arthritis usually first appears between 30 and 50 years of age, often months to years after skin lesions first occur.