It's not just sposies that have corn, although obviously those would have more direct contact with skin. But corn is literally in everything, so there is no way that you can completely shield your new little one from it. Seriously- carpet, toilet paper, paper/paper cups, plastic (including what you buy organic salad/spinach in from the grocery store), your vitamins (vitamin C, among others, is almost always made from corn), your natural soaps/laundry detergents/body products... the list goes on and on. You name it- it has corn in it.
I know that's not very encouraging, but if you're just trying to avoid sensitization I would make sure that you delay solids, you work on your own gut health, and possibly avoid top allergens yourself. I wouldn't stress myself about environmental stuff too. (That said- the prefold issue is most likely from detergent residue- which *could* be corn, or coconut, or whatever else your detergent is made out of.)
Mom to DD1 (10/07) and DD2 (3/11) I blog about our life with food allergies and eosinophilic disorders.