My Daughter's Dog Itches And Bites His Skin To The

My daughter's dog itches and bites his skin to the point of bleeding. He has dandruff as well. He doesn't have fleas and he doesn't have mange. Vet says it's allergies. I don't think so. I read somewhere about a skin disease or virus or mite or something but I can't remember what it was or where I read it. Any ideas? He's a Doxen (weiner dog).