I'd never heard of being allergic to capsicums and neither had my RN mom, and lots of people still haven't heard of it, but here I am allergic to them. I even once got served them in a restaurant after telling the waitress specifically that I was allergic to them, because she "thought [I was] kidding." I haven't experienced shortness of breath or anaphylactic shock--yet--but I still have an anaphylactic reaction: horrible stabbing stomach pains, sweating, vomiting, fever, puffy eyes, itchy mouth. I know someone allergic to onions. It's a real thing.