I can certainly testify to this one. My DH has eaten apples, peaches, carrots and nuts his whole life, but in the past 2 years has developed serious allergies to all of them (verified through allergy testing). Now if he eats even a little of any of those foods, his throat starts to swell. I now have to keep Benadryl around the house just in case he licks his fingers without thinking after cutting an apple for one of the kids or eats something with nuts in it without realizing it. It's really scary since the reaction can be severe enough to kill him if he doesn't get that Benadryl into him quickly. He's 39.
This year I'm even having a bad time with sinus congestion and itchy eyes (I'm thinking from tree pollen since that's all that's around right now) and I haven't noticed it before. At first I thought it was a cold, but colds don't last for 2 weeks and yesterday my eyes started to itch.