Skin Prick Tests

Can skin prick tests sensitize a patient to an allergen that they have never been exposed to?
I am concerned that while my son tested negative for everything but peanuts, could he now have reactions when he eats those new foods for the first time?

I keep reading that a negative skin prick test is 95%+ predictive of not being allergic but does that change if you have never been exposed at the time of your test?
Thanks