Psoriasis is a chronic immune system disorder that causes raised, red patches with a silvery white surface made up of dead skin cells. These are called plaques and they may be itchy and painful.
Psoriasis most commonly appears on the scalp, knees, elbows and torso. But psoriasis can develop anywhere, including the nails, palms, soles, genitals and, rarely, the face.
Psoriasis can range from mild to moderate to very severe. About 80 percent of those diagnosed with psoriasis have plaque psoriasis, making it the most common form of the disease. Other types include:
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Guttate [GUH-tate], characterised by small, dot-like lesions
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Pustular [PUHS-choo-ler], characterised by weeping lesions and intense scaling
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Inverse, characterised by psoriasis in skin folds
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Erythrodermic [eh-REETH-ro-der-mik], characterised by intense shedding and redness of the skin
If you have psoriasis, you're not alone. Psoriasis affects an estimated 125 million people worldwide. The disease occurs nearly equally in men and women, and across all socioeconomic groups. There may be a hereditary link - research has shown that when one parent is affected by the disease there is a 10 percent chance that their offspring will develop psoriasis.
Psoriasis can occur in people of all ages, but typically appears between the ages of 15 and 35.
No one knows exactly what causes psoriasis. The immune system is mistakenly activated, which causes the body to produce new skin cells much more quickly than normal. A normal skin cell matures and falls off in 28 to 30 days. But a psoriatic skin cell takes only three to four days to mature and move to the surface. Instead of falling off (shedding), the cells pile up and form lesions.
There are several known triggers that can cause psoriasis to flare up for the first time or aggravate existing psoriasis. These include emotional stress, injury to the skin, some types of infection and reactions to certain drugs.