Why does psoriasis affect certain areas more commonly?

[Lilbromy_x]

I tried Banana peel rubbing it on every day....I got fed up eating bananas just to have the peels to rub on my plaques ....it had no effect ..but we are all different... I remember my dermatologist nearly falling off her chair when I told her

But anything is worth a try,  I'm sure it must have worked for someone ...but I have never found any evidence myself  

I don't even like bananas so I would have to get my boyfriend to eat it haha. Maybe I'll skip the banana peel then ?