> Why would the body, a master of efficiency, produce IgE just for fun?

I was being punchy. “The pathway of B cell differentiation with respect to the nature and location of potential IgE+ memory cells as well as long-lived IgE producing plasma cells in allergy is still not completely understood” [1]. We do know, however, that “IgE is continuously produced to maintain constant IgE levels in blood,” and that Th2 cells can increase that baseline.

[1] https://www.mdpi.com/2073-4409/8/9/994

[2] https://www.ncbi.nlm.nih.gov/books/NBK27117/

they are saying that the body produced to to fight parasites like worms. these were a big problem for most of evolutionary history. With modern living standards, our immune systems don't encounter many parasites so they get "bored" and over react to harmless things like food. Evolution hasn't had time to adjust to the new living standards since its only been a few generations.