What about genes?

[jiml]

I also think you have to remember that going back to our grandparents, unless you have classic P with big plaques etc they may not have even gone to the doctors for it, and just assumed it was eczema or something.
It looks like you can have psoriasis all your life but it never be more than a few small problem areas so perhaps not everyone got a diagnosis.

That's very true TL and I'm sure a few scaly bumps weren't worth bothering a doctor about as there wasn't a health service in their day