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A variety of factors -- ranging from emotional stress and trauma to streptococcal infection -- can cause an episode of psoriasis. Recent research indicates that some abnormality in the immune system is the key cause of psoriasis.
But in conditions like plaque psoriasis, your immune system is not working properly. It can make too much of several proteins, including one called tumor necrosis factor, or TNF. The extra TNF can contribute to skin cells growing too quickly, and causes them to build up.laque psoriasis is a lifelong condition that causes dry, thick, scaly, red skin. About 7.5 million adults in America have psoriasis. Plaque psoriasis is the most common form.