Through years of research from one who has Psoriasis.
I tracked it down to the long proteins in Diary Products.
Cut out all Diary, and the hidden sources, like processed foods, bread, and your Psoriasis will go away.
Whole raw milk was a different thing, the long proteins were still whole and intact it passed through the body without being digested, but pasteurization, and homogenization force the milk through filters, breaking up the proteins into millions of small bits,irritating the intestine lining,causing bleeding, where as the proteins enter the body as foreign invaders, and hence allergic reaction to dairy.

& All thou I know better, those double Cheese burgers from McDucks really play havoc with my psoriasis.
But also since starting a PH Balance program, which is going from an acidic system to an alkaline one, there is much less reaction to these addicting Cheese burgers as well...he he

Using a combo of Acidic Acid one teaspoon to baking powder 1/2 teaspoon in a glass of water, ever 4 hours, you will also never catch a cold or any internal virus problems, as nothing can live in an alkaline system, if you research this subject, some acid foods become alkaline in the system, where some alkaline foods become acidic in the system, also increase your Vit C intake as we are supposed to be able to make it naturally in our body's.
See Vitamin C Foundation to read more, and the cures related to Vit C... Best of Luck.