Psoriasis is a disease whose main symptom is gray or silvery flaky patches on
the skin which are red and inflamed underneath. In the United States, it affects
2 to 2.6 percent of the population, or between 5.8 and 7.5 million people.
Commonly affected areas include the scalp, elbows, knees, arms, stomach and
back. Psoriasis is autoimmune in origin, and is not contagious. Around a quarter
of people with psoriasis also suffer from psoriatic arthritis, which is similar
to rheumatoid arthritis in its effects. Psoriasis was first given that name in
complete differentiation from other skin conditions by the Austrian
dermatologist Ferdinand von Hebra in 1841, although there are what are believed
to be descriptions of the disease in sources going back to ancient Roman and
possibly even biblical times.
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