Dogs lick to communicate and to take in their surroundings. It's a perfectly normal behavior for them.
Dogs have a sensory organ that allows them to taste and smell at the same time, providing them with more information about their environment.
Licking can express a range of emotions in dogs, from affection to submission and anxiety. It can even become a compulsive behavior.
Feet, especially sweaty ones, are full of biological information, such as pheromones. Sweat also contains salt, which many dogs find appealing.
If your dog licks your feet, your immediate response can turn this into an attention-seeking behavior, especially if they think it's a game.
Positive reinforcement training techniques can help distract your dog from licking. For determined lickers, consulting a vet or a dog trainer can help.
If your dog is incessantly licking their paws, it could be due to an underlying medical cause, such as allergies, parasites, or contact with a caustic material.