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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.
In some cases, psoriasis can also cause swelling and pain in the joints and spine, a condition known as psoriatic arthritis. Drugs that are put on the skin or those in pill form can help relieve symptoms of psoriasis and psoriatic arthritis, but they donât work for everyone.