The two main reasons that a dog licks human feet are to indicate feelings, status and. The human foot is a location in which many sweat glands can be found.
Official Disclaimer: I am not a vet, never played one on tv, this is just info I. the Discovery Channel shows where foxes, etc. lick their feet to keep cool. The evaporative action cools them. It can also be fungal, like an athlete's foot, but in dogs.
