I would try a solution with tea tree oil. Occationally (in the winter) I take a bowl with water, put 10 drops of tea tree oil in it, and then relax my feet in it for a few minutes. A nice side effect is that afterwards my feet remain dry for quite a long time. Ok, I don't play guitar with my feet, but the same effect can be achieved with your hands.
20 classical guitars, soon 21 :-D, 1 digital piano - no TV, no radio