There is a spray product that you can purchase at any pet store called Bitter Apple. It is used to deter pets from chewing on themselves. If your kittie has overall itching, you may have to take it to a vet for a cortisone injection to help with the all-over body scratching. You also need to find out why it is itchy! Fleas? Allergies? Etc. But if he/she has a specific area that is bothering it, I would try the Bitter Apple. I'm a retired vet due to an injury, but was in Vet Med for nearly 20 years. Hope this helps you!!
