There are probably many causes to psoriasis and we know that there is a genetic propensity towards psoraisis. It does appear as if there is something in the epidermis, some antigen that our immune system has to attack and it sends in the paratroopers--these lymphocytes causing this cascade of inflammation. We are at this point in time, searching for "what are the possibilities?" What are these antigens?" but they are probably far too numerous to completely identify.