Why was this questioned skipped?
This is indeed a difficult question and one that is not so easy to quantify. There are no good data to describe what it is about an individual that might cause others to react, that come from external sources. It is not clear how to address this problem, when no good explanation of the reaction is present. It is clear that is occurring to some people and I would suggest working with a local board certified allergist to try to determine causality and preventative action.