I think that all those things are "approach with caution" territory. Immune system can become sensitized not just to harmful substances, but also to ones "corr

I think that all those things are "approach with caution" territory. Immune system can become sensitized not just to harmful substances, but also to ones "correlated" with them, meaning it's likely they've been exposed to e.g. peanuts which had something bad in them and associated it with the peanuts themselves. Of course, there's also the fact that when a child is growing up in this VOC environment, their immune system never gets a chance to establish a good baseline for what should and shouldn't be in the system, and that is another reason allergies develop.