A relative ate peanut butter and gave my son a few kisses on the cheek. A little while later (15-20 ins), we saw a bunch of red bumps on his cheek. We can't rule out every other possibility but I wanted to see if its possible if this could be a sign of a peanut allergy?
I am not a doctor, but I believe so. I would call your pediatrician and do some google-ing in the meantime. And, keep your baby away from peanuts for now.
I know people have varying degrees of sensitivities and I've known friends that can have a reaction from contact with someone else that had contact with whatever they are allergic to. I don't see why babies or children would be different.
Edit: I just asked my partner, a nurse, and she says that people can react simply from the breath of another person.
I wonder if it is peanuts or something else? But still, I would be very aware of the potential for concern.
While life would be easier if you could always connect A to B, things usually aren't that simple. It's quite possible that the "bunch of red bumps" you describe were a) there already but you didn't notice, b) related to something entirely different, or c) essentially random (which describes most baby acne).
If you want to make sure, I'd just dab some peanut butter on eg. his back (basically anywhere he can't touch or lick) and leave it there for a minute. If he gets bumps again, then he's allergic; if he doesn't, then it was a fluke. And yes, this should be fairly safe to do, as severe reactions generally require contact with the eyes, nose or mouth (source, source). YMMV, I'm not a doctor, disclaimers apply, etc.