Psoriasis is a common and chronic incurable but treatable skin disorder. Plaque psoriasis is the most common form and appears as elevated plaques of red skin covered with silvery scale that may itch or burn. The involved areas are usually found on the arms, legs, trunk, or scalp but may be found on any part of the skin. The most typical areas are the knees, elbows, and lower back.
Plaque psoriasis on the elbow. Image courtesy of Hon Pak, MD.
Plaque psoriasis on the back. Image courtesy of Hon Pak, MD.
Psoriasis is not contagious but can be inherited. Research indicates that the disease may result from a disorder in the immune system (See Causes).
Approximately 1%-2% of people in the United States, or about 5.5 million, have plaque psoriasis. Up to 30% of people with plaque psoriasis also have psoriatic arthritis. Individuals with psoriatic arthritis have inflammation in their joints and may have other arthritic symptoms. Sometimes plaque psoriasis can evolve into more inflammatory disease, such as pustular psoriasis or erythrodermic psoriasis. In pustular psoriasis, the red areas on the skin contain small blisters filled with pus. In erythrodermic psoriasis, extensive areas of red and scaling skin are typical.
Pustular psoriasis. Image courtesy of Hon Pak, MD.
Psoriasis affects children and adults. Men and woman are affected equally. Females develop plaque psoriasis earlier in life than males. The first peak occurrence of plaque psoriasis is in people 16-22 years of age. The second peak is in people 57-60 years of age.
Psoriasis can affect all races. Studies have shown that more people in western European and Scandinavian populations have psoriasis than those in other population groups.
Medically Reviewed by a Doctor on 8/15/2014
Jeffrey J. Meffert, MD
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