Has anybody ever “gotten over” an allergy as they got older?

I grew up with no family or friends having allergies. I have no allergies. So, I’ve never been all that aware of what I was buying or giving to people. I know that’s not a good attitude to have. Anyways, I met my husband around 4 years ago, and he didn’t tell me that he had any allergies. Ever since we met, I am the one buying most of the food. One time, I got him some chocolates that happened to have hazelnuts in them. He can eat peanut butter, and he isn’t allergic to peanuts, but he is allergic to hazelnuts. Anyways, soon after trying one of the hazelnut chocolates, he started coughing, and said (barely managed to say): don’t worry: my throat is tightening but I should get over it. I said: omg, you’re allergic, should I call the ambulance? You are having a hard time breathing. He said no. After a while, he was able to explain that he is allergic to hazelnuts, but he’s able to control it, and in the last year or so, he said, he doesn’t have a reaction much at all. I find that weird that you can get over an allergy like that. Has anybody experienced that? I obviously try to avoid buying him things with hazelnuts.