Smudge had the same problem, so my vet suggested that I try giving him chlorpheniramine maleate (trade name Chlor-Trimeton, but you can get it cheaper in generic) 1/4 tablet (1 mg) twice a day. I just grind it up in a bit of water and mix it in his canned food (with a spoonful of nice smelly Solid Gold tuna to cover the taste) and it clears the problem right up (except when he's in a kibble-only mood!) It does make for mooshy poops, though, so you might do well to discontinue any hairball remedy you're currently using after the first day or so and make sure he's got plenty of water to drink. Make sure it's just chlorpheniramine maleate with nothing else mixed in.

When he's not eating canned food, I put a dab of hydrocortisone cream on the worst spots once a day. I bought veterinary hydrocortisone (Corti-Calm) but it smells like alcohol (ewwwww, vet's office!) and he won't let me near him with it, so I just put it on my own eczema instead and let him use mine!

Love, Columbine