Psoriasis is a long-lasting, noncontagious[4] autoimmune disease[8] characterized by raised areas of abnormal skin.[5] These areas are red, or purple on some people with darker skin,[9] dry, itchy, and scaly.[3] Psoriasis varies in severity from small, localized patches to complete body coverage.[3] Injury to the skin can trigger psoriatic skin changes at that spot, which is known as the Koebner phenomenon.[10]

Back and arms of a person with psoriasis
SymptomsRed (purple on darker skin), itchy, scaly patches of skin[3]
ComplicationsPsoriatic arthritis[4]
Usual onsetAdults[5]
DurationLong term[4]
CausesGenetic disease triggered by environmental factors[3]
Diagnostic methodBased on symptoms[4]
TreatmentSteroid creams, vitamin D3 cream, ultraviolet light, Immunosuppressive drugs such as methotrexate[5]
Frequency79.7 million[6] / 2–4%[7]

The five main types of psoriasis are plaque, guttate, inverse, pustular, and erythrodermic.[5] Plaque psoriasis, also known as psoriasis vulgaris, makes up about 90% of cases.[4] It typically presents as red patches with white scales on top.[4] Areas of the body most commonly affected are the back of the forearms, shins, navel area, and scalp.[4] Guttate psoriasis has drop-shaped lesions.[5] Pustular psoriasis presents as small, noninfectious, pus-filled blisters.[11] Inverse psoriasis forms red patches in skin folds.[5] Erythrodermic psoriasis occurs when the rash becomes very widespread, and can develop from any of the other types.[4] Fingernails and toenails are affected in most people with psoriasis at some point in time.[4] This may include pits in the nails or changes in nail color.[4]

Psoriasis is generally thought to be a genetic disease that is triggered by environmental factors.[3] If one twin has psoriasis, the other twin is three times more likely to be affected if the twins are identical than if they are nonidentical.[4] This suggests that genetic factors predispose to psoriasis.[4] Symptoms often worsen during winter and with certain medications, such as beta blockers or NSAIDs.[4] Infections and psychological stress can also play a role.[3][5] The underlying mechanism involves the immune system reacting to skin cells.[4] Diagnosis is typically based on the signs and symptoms.[4]

There is no known cure for psoriasis, but various treatments can help control the symptoms.[4] These treatments include steroid creams, vitamin D3 cream, ultraviolet light, and immunosuppressive drugs, such as methotrexate.[5] About 75% of skin involvement improves with creams alone.[4] The disease affects 2–4% of the population.[7] Men and women are affected with equal frequency.[5] The disease may begin at any age, but typically starts in adulthood.[5] Psoriasis is associated with an increased risk of psoriatic arthritis, lymphomas, cardiovascular disease, Crohn's disease, and depression.[4] Psoriatic arthritis affects up to 30% of individuals with psoriasis.[11]

The word "psoriasis" is from Greek ψωρίασις, meaning "itching condition" or "being itchy"[12] from psora, "itch", and -iasis, "action, condition".

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This article uses material from the Wikipedia article Psoriasis, and is written by contributors. Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.