Psoriasis, like many chronic ailments without any known cure, attracts the attention of unscrupulous companies aiming to make a quick buck off of people's hope. Much like the snake oil salesmen of old, they make inflated claims that are not backed up by any peer reviewed clinical trials.
I remember at an American Academy of Dermatology meeting some years back excited doctors hurridly leaving a lecture, cell phones to their ears. I stopped one to ask what the excitement was about and he told me "Skin Cap is full of Steroids"! No doubt those doctors were calling their office staffs to notify patients to stop using that medicine. You see, Skin Cap was marketed as an over the counter remedy with nothing other than Zinc on the label, ie: the active ingredient in Head and Shoulders shampoo. It worked so well, it was almost too good to be true. One doctor didn't believe that the answer to psoriasis was under our noses for decades and didn't believe the label either. He opened a can of Skin Cap and analyzed it: steroids! Strong corticosteroids with significant side effects only available by prescription. And he announced it at the above-mentioned lecture. Buh-bye Skin Cap. Lesson learned: if it sounds too good to be true, it probably is.
A careful assessment of any treatment via clinical trials large enough to give statistically significant results remains the gold standard of measuring a given treatment's usefulness.