Hi,
I have blonde highlights done with foil at hairdressers every 2 or 3 months; have never had a problem. I've had P at times, other times it's been less noticeable. My hairdresser is quite used to it, she says many people have P and even introduced me to a fellow hairdresser who has P on scalp also. So once again, you're not alone.
Any new hairdresser would do a 24 hour skin test, usually on your wrist or nape of neck, then check it next day before putting the colour on. There's nothing to worry about if its done properly.
Hope this helps,
big hugs
BB