Bacteria eat dead skin. After digesting the fat containing sweat, they release a gas. As they continue to feed on your feet, their colonies grow. The more bacteria living in dark, damp sweaty shoes and between our toes, the more gas. The result: "Whose feet is stankin' up the place?!!!" Don't be that person.
I'm guilty of having a favorite pair of shoes. Sometimes I can't help but wear them a few days in a row, but then ruh row, stinky feet, and ruined shoes. New rule: Never wear the same shoes two days in a row. Also, use antibacterial soap after removing said shoes. A scrub may be in order, I like to use a lavender mint sugar scrub. It leaves my feet feeling fresh and tingly.
Take care of your feet, you only get the one pair and you gotta make them last.