Approximately 15 percent of all allergic skin disease in dogs is caused by an allergy, or hypersensitivity, to a food ingredient. Symptoms include itchy, reddened skin; scabs and sores; hair loss in a specific area (focal) or throughout the body (generalized); chronic ear infections; and brown stains on the hair coat, caused by saliva from constantly gnawing itchy sites, especially the feet and toes.
Once a food allergy causes irritation of the skin, a secondary infection with bacteria or yeast may occur, adding to the complexity of the disease. A dog can become allergic to a particular ingredient in her diet, usually a protein.
Beef, dairy products, wheat, chicken, and pork are the most common offenders. Your veterinarian must first rule out other possible causes of irritation, such as an infestation with microscopic mange mites or an allergy to fleas, grass, or pollen. Once other causes have been ruled out or treated, a food elimination diet is used to diagnose food hypersensitivity.
Dogs become hypersensitive only to food ingredients that they have previously eaten, so – to be sure the dog’s symptoms are caused by food hypersensitivity — an elimination diet must consist of protein and carbohydrate sources to which the dog has never been exposed, including proteins such as lamb, venison, whitefish, salmon, duck, and proteins that have been altered so that the dog’s immune system cannot recognize then; and carbohydrates such as rice, sweet potatoes, and soy.
The dog must eat only the food elimination diet for twelve weeks or longer. If the dog is sensitive to one or more ingredients that have been eliminated from her diet, her skin will improve noticeably during the elimination trial.
If no improvement occurs, food hypersensitivity is not the cause. If improvement does occur, a challenge diet (in which the offending food ingredient is once again offered and the dog is observed for returning symptoms) is used to confirm the diagnosis. If the cause of a dog’s food hypersensitivity can be identified and eliminated from her diet, the prognosis for recovery from skin disease is good.
People living with a dog suffering from food hypersensitivity must remember that seemingly harmless treats can contain the offending ingredient and launch a whole new episode of skin disease for the dog. Rarely, a dog can develop hypersensitivity to a new substance, requiring that a new food elimination trial be conducted.