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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.
1 Over 50 percent of people with psoriasis will develop scalp psoriasis. 2  Chemicals used to treat psoriasis itch, such as salicylic acid, can sometimes cause hair breakage.  Psoriasis-related hair loss is not usually permanent.