While the dog may have allergies to the food this thread reminds me of Moley (my pet name for Molson the Sharpei spelling?).
Every year when it starts to get hot Moley starts to look more like a patches, loosing hair all around his face at first then on the body if his dad doesn't get him to the vet right away for his yearly meds, you can see moley going nuts scratching and his demeaner changes to agrivation (understandable). I'm not sure what causes it but when he gets his meds he is fine then the hair grows back. I will ask him what it is and what meds he gets
"Old age means realizing you will never own all the dogs and cats you wanted to."