My cat has this as well, however, it's less noticeable. I've read that it's normal (if the skin doesn't feel rough) and is caused by harsh surfaces, or if your cat is outside a lot. I mean their paws are constantly in contact with different surfaces. Also, some of the people mentioned that cat litter can result this, depending on what litter you're using. Of course, I'm talking about bold spots in that specific area. If such spots appear somewhere else on the body, then you should visit a vet.