Yes, it can build up so the next time it does kill you. That is too bad, I can't imagine being allergic to peanuts (or other nuts). My grandkids went to a pre-school where anything peanuts was banned totally for lunch and it was a synagogue school so they had their kosher rules going too. Hard to figure out what to feed a pre-schooler.

I had a reaction to penicillin when I was 14 or so but was at camp and it was confusing and I'm not quite sure but I always put it down, they make sure I know it could kill me if I had it again.