Food allergies in dogs can cause a large amount of skin redness, hair loss, pruritus (the sensation of itchiness), vomiting, and diarrhea. The good news is that it's very easy to treat this condition once it is diagnosed. Diagnosis involves conducting a food trial with the supervision of your veterinarian. It is a simple, non-invasive procedure.

Food accounts for about 15% of canine skin allergies. Unfortunately, veterinarians are finding it more difficult to diagnose food allergies. This is often the result of misinformed owners trying to provide what they think is the best nutrition for their pet.

Breeds and Gender Most Commonly Affected by Food Allergies

There is no specific breed, sex, or age of dogs afflicted by food allergy. Any dog can be allergic to food. It's important to understand that your dog can develop an allergy to food that he has eaten for a long period of time, as well.

Presentation/Signs of Food Allergies

Dogs usually show signs of being very pruritic when they are affected by food allergies. They may have red, irritated skin, crusting, and chew at their fur. This may sometimes even result in hair loss. A large portion of food-allergic dogs show only a single sign: recurrent ear infections.

Causes of Food Allergies in Dogs

The causes of food allergies and intolerances in dogs are:

An immune reaction
An immune reaction is a result of the allergen, such as chicken or diary, causing sensitization in the GI tract after it is absorbed. The body then mounts a response against the allergen and that has effects on the body. It is most often the protein source in the diet that causes a reaction in dogs. The most common of these is chicken, followed by beef, dairy, eggs and then non-protein ingredients such as wheat.
Food intolerance
A food intolerance means that your pet can't digest the food properly. This will usually result in vomiting, gas, excess feces, and diarrhea. The causes of food intolerance aren't well-understood.

Diagnosis of Food Allergy

Fleas, environmental allergens, scabies, and reactions to medications can all cause dermatological issues that appear similar to those caused by food allergies. It is important that your veterinarian see your dog, perform a physical examination, take a thorough history of the problem from you, and rule out other causes of skin conditions. The final step in diagnosing food allergies is to conduct a food elimination trial.

Food Elimination Trial

A food elimination trial is the only way to confirm a food allergy. This consists of using a special diet for a period of at least 12 weeks. If, after 12 weeks, your dog is doing better, your veterinarian may recommend that you challenge them with the old food to see if the original signs reoccur. Interestingly, dogs tend to only have an allergy to one ingredient in the food and, by eliminating that ingredient, your dog will be on its way back to health. A food elimination diet does not mean simply giving your dog a brand or type of food that is different. Many over-the-counter foods contain similar ingredients to one another. Often, owners do not believe that their pet has a food allergy because they have tried many types of food and not seen any improvement.

Types of Diets Used in Food Trials

Novel Protein Diets
A novel protein diet is one that contains a protein source that your dog has never been fed before. Meats such as duck, venison, and rabbit are usually in this category.
New proteins can be helpful in certain cases, but are starting to become problematic when trying to diagnose food allergies. One issue is that owners often are tempted to supplement the novel food with snacks and those snacks can contain the ingredient the dog is allergic to. The other issue is that these proteins are becoming less novel as dog food companies have started mixing many of them, such as rabbit, into their regular food recipes.
Molecularly Smaller Proteins: Hypoallergenic Diets
Using molecularly smaller proteins in food is another option for doing a food trial. These prescription diets have proteins so small that no immune reaction will usually occur. Examples include Hills Z/D formula, Purina Hypoallergenic formula, and Royal Canine Hypoallergenic formula. These seem to work fairly well, but they are expensive. There are also certain dogs that will still react even with these tiny proteins.

Special Considerations During a Food Trial

There are several things that you need to do at home to ensure that the results of your dog's food trial are accurate:

No food other than what is prescribed
No treats unless approved by your veterinarian
No human food
No hunting for food outside. Your dog will need to be kept on a leash during this time.
No flavored bones, treats, or toothpaste
No access to cat litter boxes
No flavored medication

Medications can be used for short term relief but they are not a cure. They can be used during the initial portion of a food trial to provide relief.

Steroids and/or an antihistamines can be used for the first week or so of a food trial in order to help with the scratching.
Antibiotics may be used for secondary infections from chewing the skin. These infections increase the level of licking and need to be cleared up before the results of the food trial can be evaluated. Your veterinarian can determine whether topical creams or oral antibiotics are necessary.

Prognosis

The prognosis for dogs with food issues is very good if the owner is willing to commit to following the rules of the food trial to obtain the diagnosis and then staying with a diet that will not cause either an immune reaction or intolerance by eliminating the offending substance.

Alternative Therapies

Essential fatty acids may help the dog's coat while you are dealing with skin issues.
Giving hypoallergenic baths may help soothe the dog's skin.
If the licking is in one area and the dog can tolerate a cone, it will help to decrease the risk of secondary infections from licking. It will also allow any topical medications your veterinarian may prescribe to stay put.
Probiotics are believed by some to help prevent and treat food allergies.

Citations:

Ettinger SJ, Feldman EC: Textbook of veterinary internal medicine: diseases of the dog and cat., 7th ed. Elsevier 2011.
Tilley LP, Smith FW: The Five-Minute Veterinary Consult: Canine and Feline, 5th ed., Wiley and Sons, 2011
This article originally appeared on https://www.doghealth.com/health/allergies/2184-food-allergies-in-dogs