Psoriasis is a very common condition, with approximately 3 million Americans affected. It can appear suddenly or gradually. In many cases, psoriasis goes away and then flares up again repeatedly over time. The disorder may affect people of any age, but it most commonly begins between ages 15 and 35. Psoriasis seems to be an inherited disorder, probably related to an inflammatory response in which the immune system accidentally targets the body's own cells. Evidence of the condition is most commonly seen on the trunk, elbows, knees, scalp, skin folds, or fingernails, but it may affect any or all parts of the skin. Normally, it takes about a month for new skin cells to move up from the lower layers to the surface. In psoriasis, this process takes only a few days, resulting in a build-up of dead skin cells and formation of thick scales.
Psoriasis may be aggravated by injury or irritation (such as cuts, burns, rashes, insect bites). It may be severe in immunosuppressed people (like those with AIDS or undergoing chemotherapy for cancer), or those who have other autoimmune disorders (such as rheumatoid arthritis). Medications, viral or bacterial infections, excessive alcohol consumption, obesity, lack of sunlight, sunburn, stress, general poor health, cold climate, and frequent friction on the skin are also associated with psoriasis flare-ups. The condition is not contagious.
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