I have an allergy that I've never heard of anyone else ever having. It's to the chemical used to neutralize caffein in beverages. I drink de-caf anything and it feels like the top of my head is going to explode. As a result, the only thing I drink while dininbg out is water. I drink coffee at home.
"De-caf" itself is usually a mis nomer, it should say, caffein-neutralized.
I spent a lot of time in organic chem labs and a few solvents, notiblably carbon tet, would ruin me for a day - felt like the top of head was being crushed while something was trying to escape.
Certain flavor enhancers (disodium insonate and disodium guaynlate) make my chest feel like it has just exploded.
Flavor enhancers used to be MSG but now they have many different names. They all affect my heart to some degree but the ones I mentioned are by far the worst.
Flavor enhancers can be and ARE in everything you eat. I am extremely careful about where I eat.