Snobinge, I hadn't thought of the products to keep your feet from sweating (called hyperhydrosis). My wife practices Dermatology and gives me all kinds of crap to use. The absolute best stuff is called Drysol. It burns a little, but if you follow the directions properly, it is awesome stuff. This can be used on armpits, hands and feet. There is also a new medication called Hydrosal which is a little less irritating, but I have only used it once and can't report on it.
I hadn't considered using it on my feet for this purpose, but I definitely will try it. This should 100% confirm if it is sweat build up vs. water permeating in vs. fancy socks and such.
BTW, she practices in the north suburbs of chicago or any dermatologist or GP should be able to prescribe these meds