Handy reminders from Newswise.com; one of the bunch:

Try lubricants and antiperspirants. For short hikes, petroleum jelly and drying powders can help. For longer hikes, antiperspirants containing aluminum chloride hexahydrate have a proven effect by reducing the amount of perspiration that can form on the skin surface.

Well, I guess you wouldn’t have any qualms about putting something on your foot that’s been in your armpit, right?