It's...hmm. [He's not exactly an expert, nor does he have any, but he thinks about how to explain this.]

Well, it's kind of a way some people get sick when exposed to certain things. Some people just don't process it the right way. For example, some people start sneezing a lot and get itchy eyes around spring time because there is too much pollen. That's not really the problem here, we should just concern ourselves with food allergies. Some people can't eat certain things that everyone else can or they'll get sick.