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What Causes Psoriasis

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Updated May 22, 2014

Psoriasis is a chronic skin disorder that affects 1% to 3% of the world's population. It is characterized by periodic flare-ups of well defined, red patches covered by a silvery, flaky scale on the extensor surfaces and the scalp. There are several variations of psoriasis but the most common type is chronic plaque psoriasis. The exact cause of psoriasis is unknown, but it is believed that a combination of several factors contributes to the development of this disease.

Genetic Causes of Psoriasis

Researchers have found 9 gene mutations that may be involved in causing psoriasis. One of these mutations on chromosome 6, called PSORS-1, appears to be a major factor that can lead to psoriasis. Mutations on genes cause certain cells to function differently. With psoriasis, these mutations seem to largely affect T-helper cells.

Immune System Causes of Psoriasis

In a normally functioning immune system, white blood cells produce antibodies to foreign invaders such as bacteria and viruses. These white blood cells also produce chemicals that aid in healing and fighting infective agents. But with psoriasis, special white blood cells called T-cells become overactive.

These T-cells "attack" the skin and set off a cascade of events that make the skin cells multiply so fast they start to stack up on the surface of the skin. Normal skin cells form, mature, then are sloughed off every 30 days. But in plaque psoriasis the skin goes through this whole process in 3-6 days.

Normally T-cells produce chemicals that help heal the skin. In psoriasis, T-cells produce an abnormally large amount of these chemicals and actually cause more inflammation in the skin and joints.

Environmental Causes of Psoriasis

Not everyone who has these gene mutations gets psoriasis and there are several forms of psoriasis that people can develop. Certain environmental triggers play a role in causing psoriasis in people who have these gene mutations. Learn more about other psoriasis triggers.

Sources:

De Rie, Menno, Amber Goedkoop, and Jan Bos. "Overview of Psoriasis." Dermatologic Therapy 17(2004): 341-9.

Schon, Michael, and W.-Henning Boehncke. "Psoriasis." The New England Journal of Medicine 352(2005): 1899-912.

Smith, Catherine, and JNWN Barker. "Psoriasis and its management." British Medical Journal 333(2006): 380-4.

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