I agree with the Tea Tree shampoo. I have also found a Head and Shoulders that works for psoriasis. It's a dark blue bottle. The call it clinical strength. It's been a life saver for me. I have really dark hair and the second I break out everyone knows.
I've been using MG217 for several years now also and it's all I need for my scalp. Yes, Walgreens stopped carrying it, but it is available on Amazon.com. For about 30 years nothing worked--I used tons of betamethasone daily, which barely helped the itch and caused my hair to thin in places. The MG217 has been a godsend! I use it 3 - 4 x per week-and leave it on for a few minutes. It stinks, but its worth a try for anyone who's tried everything else that doesn't work.