I suffer with psoriasis mainly on my scalp and tried all the lotions and potions that the doctor prescribed over many years. Most things prescribed, including cocois, didn't work until i tried a combination of dovonex scalp treatment prescribed by doctor and head and shoulders shampoo. Worked a treat. I now use only head and shoulders and my scalp has been fine for about a year, although the minute I use conditioner it comes back.
Hope this helps as I know psoriasis is horrible to have.