There are books on the history of nut allergies.

Having googled a look at same, another thing is being fingered.

The author [with a long list of letters after her name] of one of them says the cause she's found is too shocking to come out with without the reader taking in some of the background.

She suggests that the contents of some injections against other diseases now contain elements that enable particular foods, peanuts for example, to get thru our immune system.

Put that another way, some medines, designed for one event, as a byproduct can weaken the immune system to invaders from elsewhere.

This is therefore a variant of the excessive hygiene effect.

The myth of the Hydra springs to my mind.