We cannot always see the fleas. For every one that we might see, there's another 20 in hiding. Have you treated him for fleas recently? Best product is one like "Advantage" or similar, from a vet (not supermarket products - the chemicals in them can cause reactions). If it's definitely not fleas, he may have allergies causing skin irritation from diet. A lot of cats are lactose intolerant so can't have any dairy products that we would use i.e. Milk, cheese, ice-cream etc. Do you give your cat cows milk or cheese? If so, replace with milk specifically for cats (from pet food aisle at supermarket) ~ it has the lactose removed and so wont cause allergies and/or eczema. Boredom can also result in persistent licking and scratching. If de-fleaing and removing dairy products don't help it would pay to have a vet check him over. All the best...
It may have allergies or dry skin. Try shopping for a good shampoo first. Then if there is no relief then call a vet and ask about allergies.
Simply because the cat is delusional and thinks it's a dog.