The primary reason dogs scratch when they do not have fleas is allergies. Some pets are allergic to environmental factors, while others suffer from allergies to their food, according to the ASPCA. Dogs that scratch continually due to allergies sometimes develop secondary infections from yeast or bacteria, which cause the scratching to increase.
According to PetMD, animals suffering environmental dermatitis experience itching, hair loss and skin rashes. Lawn grass is a common cause of such allergies. Dogs that swim in ponds or stay outside in the rain often experience hot spots or moist eczema. Hot spots are more common in dogs with heavy coats or with coats that tend to form mats. The ASPCA recommends regular vacuuming of dog bedding to reduce environmental allergens. Weekly bathing helps to eliminate allergens that collect on the coat.
Scratching is a common sign of a dog's food allergies. The ASPA indicates that veterinarians diagnose food allergies by changing the pet to a prescription diet. During the time the dog is on this diet, it cannot eat any treats, table scraps or flavored medication. After the initial 12-week period, the owner reintroduces old foods to determine which ones cause the scratching and itching. After the testing period, the vet recommends a diet that eliminates the foods that cause itching, although this often requires a home-cooked diet for the dog.