By: Dr. Kari Lyon with the Veterinary Medical Center of Easton
Could the food that your dog is eating be the reason for his/her constant scratching and licking, or chronic
ear or skin infections? In some cases, the answer to this question is YES. Food allergies account for only
about 5 to 10 percent of all allergic reactions in our pets, but can be very irritating to the animal and very
frustrating for owners.
An allergy is a state of hypersensitivity to a substance, usually a protein, which is perceived by the body
as foreign. The substance in question is called an allergen, and it induces the immune system to
“overreact.” A food allergy is when the pet’s immune system reacts to a component of their diet. The
allergen in question is usually a major protein or carbohydrate ingredient in the diet such as beef, chicken,
pork, corn, wheat or soy. Occasionally there are minor food ingredients such as preservatives or dyes
that may act as potential allergens.
Food allergies usually develop within the first 1-3 years of life but can be seen in younger animals.
Because it takes more than one exposure to an allergen for the body to produce an allergic reaction, food
allergies typically form in response to a food ingredient that they have been fed for a long time. Food
allergies can manifest themselves in many different ways and can resemble other types of allergies. Most
commonly, signs of food allergies include itchy, inflamed skin usually noted around the pet’s ears, face,
feet, armpit and groin. Chronic ear infections and skin infections can be caused by underlying food
allergies. Less commonly, food allergic animals may experience vomiting, diarrhea anal gland infections
or flatulence in conjunction with the more commonly seen skin problems. Bacterial infections of the skin
are often induced by the constant scratching and biting.
Because food allergies can mimic other types of allergies, the first thing your veterinarian will do is get a
complete medical and dietary history as well as perform a complete physical exam. Other more common
causes of allergies must be ruled out. Food allergies often continue all year as opposed to other causes
of allergies that tend to be seasonal. Diagnostics that will be performed may include skin scrapings,
laboratory tests to detect flea allergy dermatitis (the most common causes of allergic skin disease),
inhalant allergies, or seasonal allergies to allergens such as pollen, mold spores or dust mites.
Occasionally skin biopsies may be needed to further characterize the allergic skin disease.
To definitively diagnose a food allergy your veterinarian may choose to perform an elimination diet. The
elimination diet can serve as both a diagnostic test as well as treatment. The purpose of the elimination
diet is to determine which, if any, part of your pet’s diet is causing the problem. There are 2 types of diets
that can be used for an elimination diet. The first is called a novel protein diet. The diet consists of one
protein source and one carbohydrate source that your pet has never been exposed to. It is important for
you veterinarian to have a very thorough dietary history for this purpose. A novel diet can either be
prepared at home by following very strict dietary recommendations or can be purchased from your
veterinarian. The other type of diet that may be chosen for your pet is a hydrolyzed diet. A hydrolyzed diet
is a complete diet that consists of proteins that have been hydrolyzed, or “broken down” so small that
your pet’s body will not mount an immune response against them. This type of diet can also be purchased
from your veterinarian. The type of diet chosen for your pet will be determined by you and your
Whichever type of diet is chosen, your dog will need to eat only that diet for a period of 10-16 weeks. It is
extremely important that your pet be fed only their special diet and nothing else. This means that your pet
can no longer have treats, rawhide, or table food. Some dermatologists also recommend that you do not
give flavored medication such as beef flavored heartworm preventative. It is also extremely important that
everyone living in the household or coming into the household be aware of the special diet that your pet is
on and that they follow your rules as to what your pet can/cannot eat, very closely.
If the signs that your pet was previously demonstrating clear up while on the elimination diet than you can
assume that your pet was indeed allergic to something in their old diet. Some dermatologists recommend
that ingredients from the old diet be individually introduced back into the diet to determine which part of
the diet your pet was allergic to. If the signs return within 7-14 days, then you can be sure to avoid this
ingredient in the future. Other dermatologists recommend continuing to feed the elimination diet as long
as it is a complete diet and your pet is doing well. Whether to introduce individual ingredients or not will
be determined by your veterinarian and you.
There is no cure for food allergies but they can be managed by avoiding the offending allergens. Along
with the diet change, your veterinarian may choose to treat your pet symptomatically with antihistamines,
steroids, or antibiotics for secondary bacterial infections. Many animals have more than one underlying
allergic condition at a time. Food allergies and allergies in general can be very frustrating diseases to deal
with. However, a long term commitment on the part of the owner and veterinarian may eventually lead to
a more comfortable pet