By the way, my wife suffered from Psoriasis until about 6 years ago when she stopped using soap and used Alpha Keri which is a liquid, non allergenic cleanser. She has about 99% success, but it came back when she used soap. She swears by it and has recommended it to many sufferers and they have had success too.
I had dandruff all my life and since I have used Alpha Keri for washing my hair I have not had dandruff for years.