Neem and manuka are both good suggestions, however Emu Spirit emu oil is excellent for psoriasis, internally and/or topically. Make sure you get Emu Spirit as their oil is far more potent than other emu oils - but no more expensive. You can reach them at emuspirit.com. I've used their oil for arthritis and recommend it highly.
The search for people who can answer your question continues for as long as needed - until you find the answer you were looking for.
When an answer is posted by someone who was invited (byYedda or by yourself) to answer your question, their answer is marked with a yellow "invited by Yedda".
To be invited to answer other people's questions in your areas of knowledge and interest, be sure to list your favorite topics:
» My Settings My Topics.
Of course, the more helpful your answers are, the more likely you are to be invited to future questions...