We have two dogs, a 3-year-old beagle-boxer mix and a 10-year-old rottweiler-chow-lab mix. Last summer they developed the same habit of chewing on themselves. The older one lost patches of hair on either flank, along the majority of his tail, and thinned hair in various spots on his legs. The younger one lost hair on his rump and around the base of his tail.
I managed this with weekly oatmeal baths, and using some sulfur-based skin ointment (just sulfur and oil, which worked great on our horse) we fixed the problem; the dogs stopped chewing, and the hair grew back.
This summer its back. The baths calm then for a day, and the younger one will lick the sulfur product off (i guess he's that itchy). The hair is gone worse than before, and they both have scabs all over. The younger one has actually learned to scoot around the rug while on his back, to scratch.
I've tried vaseline to hydrate the skin, I used hot spot treatment (seems to work for small areas), some "tar" shampoo (dog version of Head & Shoulders?) and (not me) tried hydrogen peroxide to "clean" and then vaseline (that was for about a week). Because of the weekly baths, it shouldn't be fleas, but the one bad year of fleas, they didn't have this problem.
Even if you can't pinpoint a diagnosis, is there a reliable, healthy method or OTC product to relieve their itching?
Extra info: both dogs take brewer's yeast for coat health (recommended by vet). The older one gets liquid glucosamine for joints, and pumpkin puree for digestive health.