I'm the son of an allergist, so I know precisely what I'm dealing with.
Besides, one of my food allergies is the ubiquitous CORN*. Besides its existence in obvious forms, corn is in sweeteners, thickeners and so many other things its ridiculous. Only soy would be worse for most people.
On top of that, corn is one of my favorite veggies. Thankfully, my allergy to corn is on the lowest end of the scale. As long as I control how often and how much, I'm usually OK but for some heartburn. And rocket gas.
* My other known food allergy is chocolate. No, I haven't given that up either.
However, I apparently have one more that is unknown to myself or my father. It has affected me precisely once: I got hives from eating a dish at a national chain restaurant. It was a dish I'd had before, and actually one I cook for myself. I know what should have been in it; I know what the restaurant said was in it- nothing in either one should have affected me the way it did. There was nothing on the menu that should have done that to me. All I can guess is that my dish got contaminated with something that was not supposed to be there, possibly something not normally put in food.