Historically, herbalists and naturopaths believed that Psoriasis occurred as a result of the eliminatory organs, particularly the bowel, not effectively eliminating wastes from the body. As a result, a larger proportion are eliminated through the skin. This causes psoriasis.
Because drugs don't promote elimination of toxins through the bowel, this has been lost sight of.
The key is to promote more effective elimination of toxins through the bowel.
Something really beneficial/important for people with psoriasis, is to include a significant proportion of fresh salads and fruit in the diet.
There are also many herbs which are beneficial for psoriasis.