Hi Pete
It does seem that P does indeed have a genetic factor. It is quite common for it to run in families. However, it can jump generations or run sideways and affect cousins too..
So if the gene is passed onto you in some way, a traumatic and stressful event can 'trigger' it into becoming active. Then again, you might have the gene, it doesn't trigger and you might pass it on unaffected...
And then, of course, there are those who have no history of P in any of their family (distant or close) and they end up with it....
:-/
My experience has been that once the P appears, it is with you for life. Very few people I know have had it appear and then disappear, never to return. However, some suffer seriously severe P and others just get the odd patch on the elbow or knee...and there ups and downs in the equation too! Sometimes I have it quite badly, other times it is fine and is restricted to only moderate coverage.

It is a commonly held thought, both here and with the medical community, that stress can worsen P. I can't say myself..I have a pretty stressful time over the last few months and mine isn't too bad! Then, when I have been perfectly happy, I have been covered!
Strange condition...
Glad you have found the site. I am sure others will put their tuppence in too!
SJ