This often asked question has no good answer, but keeping your shoes aired out will help. Dryer sheets work well. A gentle wash with a toothbrush inside the shoe can remove dirt. Rock shoes do not belong in the washing machine, they come clean but they tend to shrink and become stiff. Foot powder doesn’t seem to fix the problem. Talcum powder is very slippery, not a good thing to have all over your climbing shoes. Baking soda doesn’t seem to be much better. Incense cedar works well. When we get really toxic shoes, we spray them with Lysol, it can help kill the bacteria that causes the smell.