Over the course of my 20-year experience with CLL I have experienced three bouts of food allergies manifest by hives all over my body lasting for days until I could determine the source of the allergy and eliminate the offending foods from my diet. Each occurrence began about two months after a 6-8 month course of chemo as my bone marrow was rebounding. Each time, I became allergic to a different collection of foods. The medical explanation is that the FR caused my gut to be 'leaky', and that allowed undigested protein into my blood, which stimulated an immune response from my recovering population of B-cells. Each round of chemo killed off the reacting B-cells and during the recovery period a new population of B-cells dominated giving rise to a new spectrum of allergies.
If a food allergy is suspected an elimination diet can identify the offending food, but a prick test administered by an allergist is much quicker! During one prick test my reaction to oats was so strong that I had to receive epinephrine. I had been eating granola every day. Now on ibrutinib I can eat as much granola and have as many oatmeal cookies as I want!