I’ve had hay fever for my whole life, but when I was 20, I suddenly developed allergic reactions to all kinds of fruits & vegetables! The reactions are nothing life-threatening, but the roof of my mouth gets very itchy & uncomfortable, and so does my throat - it almost feels like it’s swelling shut but I think that may just be psychosomatic … An antihistamine or eating cheese (believe it or not) helps a little and the symptoms go away in an hour or so. The symptoms DO seem to be more severe during the usual hay fever allergy season, when I’m assuming my immune system (?) is a little more hyperactive.
I’m wondering: (a) what the link between these foods is, i.e. what do they have in common that causes me to react, and (b) if anyone can explain why they would have developed so late in life?
The foods include: apples (peeled and unpeeled), pears, plums, peaches, cherries, nectarines, pomegranates, carrots, cucumbers and tomatoes, walnuts, pecans, almonds (well, really all nuts).
ALSO - (I apologize for the long post) - if these foods are cooked, baked or canned, there is almost no reaction, if any.
People think I’m weird … please tell me I’m not! 
You’re not weird, nor are you imagining anything.
It’s been known for a long time that if you’re allergic to, say, ragweed and in the middle of an attack you may “cross-react” with fruits like honeydew or other melons. If you aren’t being irritated by ragweed then maybe the melons won’t give you problems. And usually the cross-reactions are strongest to fresh fruits and vegetables.
Other cross-reactions can occur. And, in fact, you throat CAN swell shut if the reactions get worse. Doesn’t mean it will, just that it could.
If you experience ANY breathing difficulties AT ALL in these circumstances get to an emergency room IMMEDIATELY
I strongly advise that you see an allergist. You should be evaluated so you know what, exactly you are allergic to and perhaps you’ll be able to avoid it. Also, there are new treatments that didn’t exist several years ago that might give you better control over the hayfever. No havfever - most likely no cross reactions. You’ll feel better and you’ll be able to eat what you want without worrying.
Or at least you’ll know what NOT to eat if your hayfever IS bothering you.
As for why they surfaced at 20 and not earlier… you can develop allergies or new allergic symptoms at any age.
You’re not. Broomstick is right on the money. Get thee to an allergist, pronto.
Thanks!
I’m not super-concerned, just very curious about what is in these different foods that I’m actually allergic to … like what is present when they’re raw that is lost when they are cooked or processed?
I think your reason would be the actual cooking process. Cooking causes chemical changes that could eliminate the specific antigen your body is responding to.
I wish I could tell you more than “I know what you mean.” I was pretty seriously allergic as a kid, and retain just one serious allergy: potatoes, which is usual but not unheard-of. I’m actually allergic to the whole botanic family, which includes tomatoes, capiscum peppers, and eggplant. But the others I can manage if, in the first two cases, they’re very ripe (i.e. no green peppers, only red, orange or yellow) or they’re thoroughly cooked. My only guess is that the actual chemical I’m allergic to is diminishes on ripening and is heat-sensitive.
One other safety tip - be very careful in handling anything you’re allergic to. I don’t dare touch potatoes since an incident in first grade. We were making potato prints, I touched the potato and then my eyes - which swelled shut for about a day. Not fun.
Do get yourself to an allergist. Ask him or her about other potential cross-reactions, such as to household chemicals, pets, insects, or other triggers that you may not even be aware of.