It could be the food, or it's environmental issues. Roxy has it too. Mostly her front 'arm pits' but she will also do her ears, chin and face.
I home cook for her and have really avoided things that could be food related. Last year was very, very bad. She had skin infections and yeast infections and b/c she has liver issues, we could only treat with a microbacterial shampoo. I researched Aloe Vera Gel (orally) and I have been giving her 1/4 teaspoon daily, this hasn't cured her, but it has helped tremendously
I also suggest vacuuming weekly, changing detergents to the free of fragrance and dye, no fabric softener or sheets, etc...Try to eliminate and clean what 'could' be environmental factors as well as maybe trying the Natural Balance food for allergies