[Updated January 30, 2019]

When your dog itches, you know it. That relentless licking, scratching, chewing – anything he can do to relieve the itch. He seems obsessed, and he probably is. Whatever you do, don’t ignore this problem (as if you could!). Incessant scratching and chewing may indicate a food allergy. He’ll constantly tear into any place on his body that he can reach with his teeth or claws. You may see ugly hair loss. Until you find the cause, this problem will go from bad to worse. Trialing an elimination diet for dogs may be able to help with this, but it isn’t always certain the cause is a skin allergy.

Yes, persistent skin irritations can also be due to something else, including dry skin, hormonal issues, liver disease, fungal infections, drug reactions, pain, boredom, anxiety, or a combination of any of those! For this reason, if your dog has chronic itching, it’s always worth a trip to the vet to rule out some of these potential causes.

But the fact is, 70 percent of canine skin conditions are allergy-related – and most of those are due to flea allergy and/or environmental allergens, such as pollen, mold, or dust mites. If the dog has fleas, or if his symptoms have a seasonal component, it’s likely that environmental allergies are his primary problem.

But an estimated 10 to 15 percent of the dogs who suffer from allergies are allergic to their food, or at least some ingredient or ingredients within their food. Many owners assume that a dog with a chronically upset stomach has food allergies, but many dogs who have chronic upset tummies may have a food intolerance; if there is no hypersensitive immune response, it’s not an allergy. (That said, one can use an elimination diet to help determine whether the dog is intolerant of certain foods, too.)

The primary symptom of food allergies, just as with inhaled or contact allergies, is itching. Dogs with food allergies might also show gastrointestinal signs (vomiting and/or diarrhea), or secondary infections, such as chronic otitis (ear infections), but they might not; non-seasonal (year-round) itching might be their only symptom.

How to Figure Out What Your Dog Is Allergic To

Puppies aren’t usually born with food allergies. These hypersensitive immune responses tend to build up over time, usually appearing between the ages of 1 and 3 (but they can appear late in life, especially if the dog has been on the exact same diet for years and years). The most common food allergens for dogs are protein sources – especially beef, dairy products, wheat, chicken, egg, and soy – but the cause may also be a carbohydrate, a preservative, a dye, or anything else in the food.

While there are skin and blood tests that can be performed for allergies, they’re expensive and have only a 60 percent accuracy, frequently returning both false positives and false negatives. No wonder many veterinarians consider them useless! Although all you’re going to hurt by trying them is your wallet, a far better solution is an “elimination diet.”

Better described as a “restricted diet,” this limited-fare menu will help you both identify the foods that cause an allergic (hypersensitive) reaction in your dog, as well as find foods that can be fed to him without causing an allergic response.

The first step in a food-elimination trial is to think hard about all the types of food you have fed to your dog, and then gather the ingredient lists for all commercial foods the dog has received, or foods you have included in his home-prepared diet. Write down (or list in a spreadsheet) all of the ingredients in the foods your dog has eaten. While it may be difficult to recall (or impossible, in the case of dogs who were adopted as adults) every food a dog has eaten in his lifetime, all of the ingredients in the diets that the dog has received most recently should be included on the list.

You now have a working list of the ingredients you will avoid when selecting foods for the dog’s elimination diet.

Dog Food Ingredients for Allergic Dogs

The goal for the first stage of the trial is to find ingredients that the dog has never received, in order to find some to which he is not allergic. You will then start him on a diet of these “novel” ingredients, in hopes that his itching reduces and then stops, indicating he is no longer eating something to which he is allergic, and that he is not allergic to any of the novel ingredients.

If his itching and other dog food allergy symptoms stop, you can begin adding other ingredients back into his diet, one at a time. If the itching recurs, the most recently added ingredient is then put onto your dog’s list of forbidden foods.

Ideally, an elimination diet initially consists of just one protein source and one carbohydrate source, neither of which appears on the list of foods your dog has previously eaten.

“I recommend a limited-antigen diet: one protein, one carbohydrate,” says Eileen Fatcheric, DVM, co-owner of the Fairmount Animal Hospital in Fairmount, New York. “The foods should be ‘novel,’ meaning the dog has not eaten them before.”

In order to ensure the food is new (novel) for your dog, your veterinarian may recommend some seemingly crazy cuisine. Ingredients often recommended for elimination diets include:

Proteins

• Rabbit
• Venison
• Duck
• Buffalo/Bison
• Kangaroo

Carbohydrates

• Pumpkin
• Oats
• Barley
• Quinoa
• Chickpeas (also a good protein source)

Keep in mind that this initial, “one novel protein and one novel carb” diet is being used in hopes that you have eliminated whatever your dog has been reacting to in his diet, so that he stops itching, his skin clears, and any other allergic symptoms he has ceased. Once he is totally asymptomatic – and this may take weeks – you can add one ingredient to his diet for a few weeks. If he starts itching, that ingredient gets added to the “forbidden” list, and you retreat to feeding the diet that didn’t make him itch, wait until all is calm again, and then try adding yet another ingredient.

The ingredients you choose to use for this initial trial should be new to your dog, but readily available to you, and affordable. Some of the more unique proteins may be more available in frozen, dehydrated, or canned form than fresh.

Decades ago, beef was the most common animal protein used in commercial dog foods, and so when a dog appeared to have a food allergy, most veterinarians would recommend a lamb and rice food. These ingredients were rarely seen in commercial foods at the time and, therefore, were novel to most dogs. The combination was even dubbed “hypoallergenic” – a misnomer for any dog who is allergic to lamb or rice! Of course, when food-allergic dogs improved on these foods, they became popular; soon, even owners whose dogs didn’t have allergies tried them, and more companies began offering foods that contained lamb and rice. The upshot is that within a relatively short time, both lamb and rice lost that all-important “novel” characteristic for many dogs.

The same phenomenon is making it even more difficult for dog owners to find foods that contain ingredients that are novel for their dogs. The popularity of grain-free foods, and their inclusion of potatoes, sweet potatoes, peas, and chickpeas (as replacement carbohydrate sources for grains) means that many dogs have been fed these formerly rare (in dog foods) carbs, eliminating those ingredients from the pool of potential “base” ingredients for the allergic dog’s preliminary restricted diet.

Other owners may have fed novel proteins to their dogs in foods that appealed to them for reasons other than food allergies – just to provide the dog with variety, for example.
We suggest that owners avoid feeding foods that contain uncommon proteins to their dogs, so they are available for use in the dog’s diet if he should develop food allergies later.

Commercial Dog Foods for an Elimination Diet

Today, a visit to any specialty pet-supply store will reveal that any number of companies offer “complete and balanced” foods that contain uncommon proteins such as rabbit, duck, venison, bison, and even kangaroo. Further, many of them are formulated to contain only one type of animal protein – what the makers often call “limited-ingredient” formulas. Those products seem ideal for feeding a food-allergic dog, right? Well, it depends.

A commercial dog food is most likely to work in an elimination diet if it contains just one novel (to your dog) protein and one novel (to your dog) carb. However, if it contains (for example) one novel ingredient (say, rabbit) and chicken – which is the most common animal protein in commercial dog food today – it probably won’t work for use in an elimination diet. You have to look past the “headline” ingredients to see whether a food might also contain ingredients your dog has consumed many times; it doesn’t matter if a food is called “Brand X Bison and Barley Dog Food” if it also contains beef and rice.

Here’s how you can use our WDJ Approved Dry Dog Food Database to find a limited ingredient dog food. 

There is also the matter of the potential for cross-contamination at the pet-food manufacturing facility. A dog severely allergic to chicken, for example, may react to a food that contains no chicken, but was made on manufacturing equipment that was inadequately cleaned after running a batch of food that contained chicken.

Also, even if it’s a single-protein, single-carb “limited ingredient” commercial diet, any “complete and balanced” food will necessarily contain more ingredients than a home-prepared diet that contains only the protein and carb sources. While it’s quite rare that the dog’s allergy is to a preservative or herb or fiber source in the food, the fewer ingredients that are used in the trial diet, the more certain you can be about what is or is not causing the dog’s symptoms.

For more on commercial foods to feed your dog with allergies, see our companion post Commercial Foods for Allergic Dogs.

Homemade Dog Food for Canine Allergies

Another option is to make your own dog food for dogs with allergies – a course of action that has its own benefits and pitfalls. While it provides you with the ultimate method of ensuring that your dog’s diet contains only those ingredients that prove to be safe for your dog, it may take some trial and error to figure out appropriate portion sizes and the best ratio of meat to carbohydrate for your dog. Also, you may be limited as to how long you can keep your dog on the diet, as it isn’t likely to be nutritionally balanced.

It can also be expensive. When dog-food manufacturers use something like kangaroo or rabbit in their diets, they have the benefit of buying those novel proteins in bulk, for much lower prices than you are likely to pay. That’s why it can be a great boon if you’ve never fed your dog a diet that contains a common animal protein, that is, when your dog’s “novel” protein is something that’s easy to find and affordable, like fish or beef.

Feeding Allergy-Free Dog Food

The switch to the elimination diet should take place over the course of a few days. Change your dog’s food gradually, substituting increasing amounts of the new food for equal amounts of the old food until the dog is eating only the new food. If you see any signs of gastric distress (vomiting, diarrhea, constipation, which may indicate your dog is allergic to one of the ingredients you have chosen) or if your dog refuses to eat the new food, you’ll need to choose different ingredients.

The length of time that you feed the initial diet (of just one protein and one carb), and how long you should wait before introducing a new ingredient, will depend on how your dog’s allergies are expressed. Dogs whose primary allergy symptoms include diarrhea, vomiting, and gas will respond (for better or worse) relatively quickly after dietary changes are made.

However, if the dog’s primary symptom is itching, it can take a lot longer for the problem to subside after the “trigger” food is removed from his diet. It may also take longer for him to start itching again when a problematic ingredient is added back into the diet.

“For food-allergic dogs whose symptoms are gastrointestinal, you only have to do the ‘diet trial’ for two weeks,” Dr. Fatcheric says, adding that it could take as much as 8 to 12 weeks for skin problems to completely clear.

If there is absolutely no change in the dog’s symptoms – no reduction in itching or GI problems – you may want to change both the protein source and the carb source and start a new elimination trial.

If a second trial, with all-new ingredients, produces no reduction in the dog’s symptoms, it’s very likely that the dog’s diet is not what he’s allergic to; he most likely is allergic to something else in his environment.

In contrast, if your dog’s symptoms reduce immediately and disappear quickly, you will know that there was something in his most recent diet (before the elimination diet) to which he was allergic.

Challenging the Evidence

Few owners are willing to take a further step to confirm the link between their dogs’ old diet and the dogs’ allergy symptoms – a “challenge” phase – but many veterinarians feel this step is necessary. To definitively establish the link between the dog’s former diet (or even the single ingredient suspected of being the allergy culprit in the old food), some vets suggest reintroducing the old diet (or the suspect ingredient); if the dog begins to break out in itching or GI distress, the allergen for that dog is decisively confirmed. Quickly return to the diet that your dog did well on, with no allergy symptoms.

Some owners stop there – and who can blame them? It’s a pain to employ such scrupulous supervision over your dog’s diet. If you feel confident that the trial and challenge have identified the ingredient that is problematic for your dog, you can start looking for (or formulating) a new, complete and balanced diet that is free of that ingredient.

However, it can be incredibly useful to continue for a few more weeks, to challenge your dog with a few more ingredients (one at a time), in hopes of finding more ingredients that are safe for him to consume. Feed him the trial diet until his allergy symptoms are gone again, and then add one ingredient that you would like to use in his diet in the future. If you are able to add it and he doesn’t react with signs of allergy within two to three weeks, you can put that ingredient on his “safe” list for now. Once you have challenged his system with a few proteins and carbs without an allergic response, you should have enough ingredients on his “safe” list to enable you to buy or build a complete and balanced diet containing those ingredients (and none of the ones that he’s proven to be allergic to).

If you’re lucky, you may be able to find a commercial diet that contains only the ingredients on your dog’s safe list and none of the ones that trigger an allergic reaction in your dog. But if you can’t find such a diet, or want to continue to prepare your dog’s diet at home, Dr. Fatcheric recommends that you “work with a veterinary nutritionist to make sure your diet is balanced and complete.” Another option is to consult with a company like JustFoodForDogs, which will formulate a diet based on your dog’s special needs. (See “Better Choices for Home-Prepared and Special Needs Recipes,” December 2013.)

Tips to Ensure Clear Results

Make sure your dog consumes only the “trial” food – even for treats. For training treats, use dried bits of the animal protein you are using in the trial. (See “How to Make High Quality Dehydrated Dog Treats” in the May 2012 issue of WDJ.)

Be sure to check any medications your dog may be on, such as a monthly heartworm preventative, to make sure they have no flavorings. If they do or you’re not sure, ask your veterinarian for an unflavored alternative. It is critical that you are vigilant about your dog’s diet during this time.

If you have several pets, you’ll need to oversee dinner time to ensure your dog doesn’t eat someone else’s meal. Or put all the dogs in the household on the same diet for the trial period. With an elimination diet, your dog can’t even lick the cat’s bowl clean or gobble down something he finds outside. You’ll need to watch everything he does. This is another time when it’s valuable for your dog to be happy and habituated in a crate for the periods when you can’t supervise him directly.

“I myself would have a hard time being completely compliant for two to three months. No treats (of foods that aren’t part of the diet). No nothing. Be careful in homes with toddlers who drop food on the floor. And watch for well-meaning neighbors or in-laws slipping a treat,” Dr. Fatcheric says.

Dog Food-Elimination Trial Proof

A food-elimination trial can be a valuable tool in determining the cause of your dog’s discomfort. But it does take commitment, vigilance, and a little extra cash. It’s well worth the effort, though, if you do it correctly.

If you stick with the restricted-diet regimen, you should see a reduction in itching by 50 percent or more at the end of the trial. If not, you haven’t eliminated the cause. That means you either need to try another combination, consisting of a new protein and new carbohydrate, or determine that dietary hypersensitivity is not the issue. That’s why it’s so important to involve your veterinarian right from the start.

If the results do prove a dietary cause, you will have been given the key to an itch-free, happy, comfortable dog. You can then either choose a commercial food that contains only those ingredients you used during the elimination trial or consult a veterinary nutritionist to construct a diet that will work for your dog. It’s important that the dog’s diet for the long-term is complete and balanced.

“Diet trials are hard. But the people with food-allergic dogs who successfully complete them potentially have a comfortable, itch-free pet without expensive and potentially harmful medications. It’s worth it, if you can tough it out,” Dr. Fatcheric says.

Cynthia Foley is an experienced dog agility competitor.  Also a lifelong horsewoman, she served as editor of Horse Journal from its inception in 1994 to 2014.