I have psoriosis on my scalp. I haven't found many things that work long term and I get a lot of differing solutions.
I use coal tar shampoo, which is now banned in some states as it causes cancer. I use it sparingly.
I used Nizoral but had to stop as you can't use that and take Neurontin at the same time. Check for drug interaction with any medicated shampoos. There is a handy drug interaction site on the net.
My husband has it on his legs and swears by Ponds Cold Cream. It really does work for him.
Stress plays a HUGE factor in the break out of it.
I thought that I had it on my scalp at one point but it turned out to be a yeast infection on my scalp so I had the doc give me a special shampoo which cleared it right up.
However, I do have it on my scalp. Sun works great for it so I sit out for 15 minutes to a half an hour in the full sun each day. That only seems to work on the part line and I have long hair.
I have about six different shamoos going in my shoulder right now that I rotate through.
What works for one person might not work for the next and you have to keep changing even if you find something that works.
MG216 is a tar based shampoo that the pharmisist will order for you at Wal Mart. It is an over the counter shampoo. It also comes in a oil based gel. Pretty smell, but very effective.
Are you sure that it is psoriosis? If so, the sun is out and sun is great for relieving this.
Join the Psoriosis foundation. You can find them on the net and they send out newsletters