Does the skin in this area look normal?
Have you checked your cat for fleas?
Yes, fleas could indeed be the problem. Some cats are extremely sensitive to them, and even suffer allergic reactions to the bites even if they only have a couple fleas. I would recommend getting a topical product from a veterinarian as these are safer and work better than the discount store brands. Frontline or Revolution are both very effective. You need to use whichever one you choose for three consecutive months to break the fleas life cycle. You could also get a pill called Capstar that does a quick kill of any adult fleas that are on your cat at the time its given. It can be used along with the topical product if you want.
If your cat continues with this behavior even after there is no sign of fleas at all then it could be a disorder called hyperesthesia. Hyperesthesia is a condition where basically the cat's skin is too sensitive. It is diagnosed by ruling out other medical conditions, such as allergies, fleas, skin infection, etc. Here is a link to a page about this disorder:
Treatment for this problem includes providing a stress free environment for the kitty, providing him with lots of interactive toys to play with, and possibly prescription anti-anxiety medications. You can also try a product called Feliway which consists of calming pheromones. Its comes in a plug in diffuser, and most larger pet stores carry this product.
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