If you are allergic to oranges, wouldnt this mean you have a fructose intolerance? Is there fructose in oranges? Sorry if that is a dumb question! I've actually never heard of an orange allergy!
People can be allergic to pretty much anything
But in the case of the food intolerances we develop with ME, it's more likely to a be a leaky gut or similar issue, allowing proteins to leak out of the gut and into the bloodstream, where they are recognized as foreign and attacked, causing an immune reaction.
It's not really an allergy, although it is an immune reaction. Bad news is that we can start reacting to pretty much anything at any time. But the good news is that if the leaky gut is healed somehow, it might be safe to eat those foods a gain some day.
I'm also reactive to egg yolks and dairy, as well as cranberries, broccoli, pineapple, banana, pecan, and sesame, according to IgG tests. I also react to egg whites and gluten, though it's a different reaction (faster, more intense swelling, and of shorter duration), and the test didn't pick those up.
It's pretty hard to guess what's going on, but it seems like something pretty complicated.