Psoriasis is a chemical imbalance between 2 enzymatic regulators cyclic adenosine monophosphate (cAMP) and cyclic guanidine monophosphate (cGMP). Normally cAMP is dominant, but in psoriasis cGMP becomes dominant, and this increase of cAMP is responsible for the increased cellular division seen in psoriasis.
Levels of cAMP can be elevated with various herbs. My favorite choices are coleus forskohlii and zizyphus seed. To protect the breakdown of cAMP by a liver enzyme you can add yerba mate', watercress or nettle leaf with the forskohlii or zizyphus.
Other factors that can be involved in the formation of psoriasis include poor digestion, liver insufficiency, and nutritional deficiencies, especially omega 3 fatty acids, and antioxidants including vitamin A, zinc and selenium.
Digestion and liver problems can be assisted by the use of digestive bitters. Digestive bitters are bitter tasting herbs, usually sold in liquid form since they must come in to contact with the tongue to work. Bitters work by stimulating the bitter receptors on the back of the tongue. This in turn stimulates a nerve, known as the vagus nerve. This in turn increases the production of stomach acid, bile secretion and pancreatic enzyme secretion. They also have a cleansing effect on the liver, and the bile increasing effects make it useful for dissolving cholesterol based gallstones. Since bitters do cleanse the liver it is important to drink a lot of water throughout the day when using them. You only need to taste bitters for them to work, so only small doses are needed. Generally I recommend 1/2 dropper full 2 to 3 times daily, preferably before meals.
There are differences in structure between the omega 3 fatty acids found in fish oil and flax oil. Fish oils are more beneficial, though their intake must be kept limited due to the high levels of vitamin A also present. So I recommend omega 3 supplementation with both fish and flax oils.
As for the antioxidants I recommend no more than 10,000IU of vitamin A, 50mg zinc, and 600mcg selenium daily.