Will have to defer to the expert,AP,however most of us are sensitised to some allergen but never have anaphylactic reactions.
When my boys were younger we got into farming ,as a hobby ,and the three of us are now allergic to rye grass (in it's season) something none of us was allergic to before. The culprit was most likely many seasons of cutting, baling and stacking hay.
Incidently one son, who was a researcher some years ago at Penn State Uni., said it was thought that it was most likely the preservative in (injected) drugs that produces anaphylaxis in some persons.
