If the skin on his back is inflamed and/or flaky to go along with the hair loss he may be suffering from a flea allergy. Some animals are highly allergic to flea saliva and even one bite can trigger a reaction. The itch is so bad that they obsessively scratch and/or chew at the irritated spots obsessively. I have 2 dogs with flea allergies and I've had people think they have mange before because of the hair loss.
If you suspect fleas, grab some blue Dawn dish soap and some body armor to give him a bath. Make sure you treat the carpets for fleas as well (flea carpet powder is about $5 at wally world) and wash any bedding or toys. Make sure you treat the yard too. Flea killer spray (the kind that attaches to the water hose) is about $10 at wally world. I hope this helped.. I hope he gets to feeling better :)
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