Psoriasis is a long-lasting autoimmune disease characterized by patches of abnormal skin. These skin patches are typically red, or purple on some people with darker skin, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to complete body coverage. Injury to the skin can trigger psoriatic skin changes at that spot, which is known as the Koebner phenomenon.
There are five main types of psoriasis:
Plaque psoriasis, also known as psoriasis vulgaris, makes up about 90 percent of cases. It typically presents as red patches with white scales on top. Areas of the body most commonly affected are the back of the forearms, shins, navel area, and scalp. Guttate psoriasis has drop-shaped lesions. Pustular psoriasis presents as small non-infectious pus-filled blisters. Inverse psoriasis forms red patches in skin folds. Erythrodermic psoriasis occurs when the rash becomes very widespread, and can develop from any of the other types. Fingernails and toenails are affected in most people with psoriasis at some point in time. This may include pits in the nails or changes in nail color.
Psoriasis is associated with an increased risk of psoriatic arthritis, lymphomas, cardiovascular disease, Crohn disease, and depression. Psoriatic arthritis affects up to 30 percent of individuals with psoriasis.
Psoriasis is generally thought to be a genetic disease that is triggered by environmental factors. 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 non-identical. This suggests that genetic factors predispose to psoriasis. Symptoms often worsen during winter and with certain medications, such as beta blockers or NSAIDs. Infections and psychological stress can also play a role. Psoriasis is not contagious. The underlying mechanism involves the immune system reacting to skin cells.
Psoriasis is estimated to affect 2–4% of the population of the western world. The rate of psoriasis varies according to age, region and ethnicity; a combination of environmental and genetic factors is thought to be responsible for these differences. It can occur at any age, although it most commonly appears for the first time between the ages of 15 and 25 years. Approximately one third of people with psoriasis report being diagnosed before age 20. Psoriasis affects both sexes equally.
Psoriasis affects about 6.7 million Americans and occurs more frequently in adults.
Psoriasis is about five times more common in people of European descent than in people of Asian descent.
People with inflammatory bowel disease such as Crohn disease or ulcerative colitis are at an increased risk of developing psoriasis. Psoriasis is more common in countries farther from the equator. Persons of white European ancestry are more likely to have psoriasis and the condition is relatively uncommon in African Americans and extremely uncommon in Native Americans.
There is no cure for psoriasis; however, various treatments can help control the symptoms. These treatments include steroid creams, vitamin D3 cream, ultraviolet light and immune system suppressing medications, such as methotrexate. About 75 percent of skin involvement improves with creams alone.
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