Hi there. Welcome to YT. My mom was born in Sylacauga and my husband went to Auburn (just an aside
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My big girl had some back irritations too. I switched to yorkie splash and shine ..which has a higher PH and it went away.
This was after the vet did skin scratches and tested for scabies, yeast bacteria and other pests.
I sure hope you find a solution for your kid. Sometimes it seems skin issues are the hardest to find a cause/solution