I've been doing some reading on the trusty internet (oh, what did we ever do without it?), and have so far seen this:
- an allergy is an immune system response to the irritant, and an intolerance is a digestive system response
- an allergy is most often manifested with respiratory symptoms or hives, whereas vomiting is more commonly associated with intolerances
- with an intolerance you can normally eat some amount of the food without ill effects
- a food intolerance commonly shows up as a delayed reaction, and it can be difficult to determine which food caused it
"They" also say vomiting is a "mild" response - I suppose if one is comparing it to anaphylaxis, then that is true. It certainly didn't seem mild at the time.
Some things I've read say you can introduce nuts as early as 12 months; others say to wait until after age 4 because nuts can be so highly allergenic. The doctor seemed to think Noah's digestive system was just too immature to handle them. There is some support for that idea - Noah didn't start solids until 7 months because he wasn't ready, and didn't eat foods with even the tiniest chunks until after 12 months because he choked on them, but in this case the reaction was so instant that I'm not totally convinced this is the answer.
So we'll see what the allergist says... the doctor didn't seem to think this necessitated a trip to the allergist, but we'd rather hear for sure from a specialist whether it was a fluke, or due to his age/digestive system's development, or whether we need to have Noah avoid eating cashews, or all tree nuts, and know to just what degree we need to be concerned about this.
On the bright side, it looks like we don't have to worry about our friends' kids catching this!