Excessive paw licking can be caused by injury, allergies or anxiety. Treatment will vary based on the cause.
Injury
If your cat is excessively licking his paws, first check his paws for any signs of injury. Excessive licking of an area often indicates pain that the cat is trying to treat.
Look for stickers, burrs or splinters stuck in the foot. Look for cuts that may need to be treated. If there is no injury readily apparent, move the paw around to look for swelling or additional pain. Your cat may have pulled a muscle or bruised his foot playing or jumping off an object. If you notice pain or swelling that seems to persist, consult your veterinarian.
Parasites
Animals often excessively lick areas that have been infested with parasites such as ticks or fleas. Check your cat's paws for ticks.
If there are no ticks, he may have a flea bite. Even you don't notice fleas on him, a cat with flea allergies can be affected by a bite for several weeks. If you notice any black flecks on your cat, he's been in contact with fleas, so give him flea preventative to prevent future infestations and clean your house to remove any remaining larvae.
Allergic Reactions
Cats can be allergic to food or environmental pollens that may cause them to itch excessively. Food allergies often cause cats to lick their paws, though the cause could also be environmental.
If you've recently changed food or treats, this may be the cause. If not, you may have to visit a dermatologist to determine what's causing the allergic reaction.
Switch to a high quality cat food with no preservatives, artificial coloring, grains or meat byproducts. These are all cheap fillers that your cat can't digest anyway. If your cat is allergic to a preservative or coloring, it will be very hard to determine, so purchase a food that doesn't utilize these ingredients.
Once you have your cat on a high quality food source with simple ingredients, try different protein sources to see if your cat does better on some foods than others.
Anxiety
If all medical causes have been eliminated, your cat may be excessively licking his paws because of a psychological illness, such as anxiety or obsessive-compulsive disorder.
If you have recently made a major lifestyle change, such as a new roommate, pet, baby, job or home, your cat may be stressed and anxious. This can exhibit itself through nervous behaviors such as excessive paw licking.
To reduce this behavior, install a DAP diffuser, which releases calming pheromones in the air. Give your cat a calm room with a DAP diffuser, soothing music, comfortable hiding places, toys and no other visual stimuli. Allow him to go in there and relax.
Spend extra time interacting with your cat and establish a consistent routine to allow him to adjust to his new life.
If the problem persists, it may be an obsessive-compulsive behavior that requires medication for treatment. No matter what the cause, excessive paw licking can become a stressful habit for both you and your cat.