Hi,
Yes, I think you SHOULD take him to the vet and I'm glad you're planning on doing that tom'w! : )
From your description, it does sound like he may have a parasite problem and just because he's an indoor-only cat, doesn't mean he can't get fleas. They can be brought in to the house on people's pant legs or shoes. It just takes one!
He either is having an allergic reaction to the flea bites (saliva) or has another type of skin allergy or condition. There are many types of skin conditions cats can get, so bringing him to the vet to find the cause is very smart!
Have you combed him and parted his fur looking for fleas at all? Have you looked at his skin under the fur at the base of the tail? There's a condition called 'stud tail' which is similar to feline acne (plugged oil glands) which can occur at the base of the tail. The vet will find the problem and if it's a 'phantom' problem, will most likely give him a shot of Prednisone (steroid) and/or an antihistamine to stop the itching.
Please let me know what the vet says and I hope your boy is relieved of this annoying symptom, real soon! Good luck tom'w!
Cher : )
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