I have to agree with CY and Em on this one - whatever I eat or drink very much reflects in my skin....
I'm not totally sure about the things common to all sufferers, I'm thinking more along the line that everyone has to find out for him/herself what triggers the P :-/
As Em says, there are a couple of things that are regarded as being generally bad: all nightshade veggies (potatoes (true for me), tomatoes, eggplant (not true for me

) ), sugars, processed foods, and alcohol.
I find alcohol as such is not so much a problem, as beer all on its own.... makes me flare up big time :-/

Des