Guest contributor, Carlotta Cooper of DogFood.guru

Is your dog scratching like crazy? Is his skin red? Is he losing hair? With symptoms like these, pet owners often think, “Ah ha! Rufus has fleas!” Or mange, or another pest or skin problem. But if you rule out fleas and obvious pests, you'll sometimes find that your dog has a food allergy.

It's estimated that about 10 percent of allergies in dogs are due to food allergies. That makes them the third most common cause of allergies in dogs, behind flea bite allergies and inhalant allergies (things like pollen). They're a common cause of itching and scratching in dogs.

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What are the symptoms of food allergies?

Dogs with food allergies typically display the symptoms described above. They will scratch, make their skin red and raw, lose hair, and can become bald in patches. They can develop hot spots and skin infections in the places on their skin they have damaged. Sometimes they also develop ear infections. The most common places for dogs to show signs of skin damage are on their face (which they often scratch or rub with their paws), their paws (which they often lick), their forelegs, armpits, and their tail area.

Dog food allergens

If your dog has a food allergy, it can be hard to diagnose and control, depending on what your dog happens to be allergic to. The most common food allergens are some of the most common ingredients found in dog foods: beef, dairy products, chicken, lamb, fish, chicken eggs, corn, wheat, and soy. None of these ingredients are really “bad” foods. Most dogs can eat them without any problems. There's nothing wrong with chicken or fish or eggs, and so on. They are simply found in so many dog foods today that some small percentage of dogs have become allergic to them.

Diagnosing a food allergy

If you do have a dog with a food allergy, you can talk to your veterinarian about trying your dog on an elimination diet. This kind of diet puts your dog on a very simple diet with just one protein which he hasn't eaten before. Then you can introduce different things to his diet, one at a time, to see what causes a reaction. This method takes some time but it's the best way to figure out exactly what your dog is allergic to.

Some people try to guess what their dog might be allergic to and try different dog foods, hoping they will get a food that their dog can eat. This method might work for a while but in the long run, it's usually less successful and ends up costing more money since you'll have to discard a lot of expensive dog foods your dog can't eat.

No matter what your dog is allergic to, there are lots of great dog foods available today. Once you know what is triggering your dog's allergy, you should be able to find a good food that he can eat. If there's nothing available from your local pet food store, there are some very good prescription diets for dogs with allergies. They cost more but your dog will be able to eat and the skin problems will clear up. Fatty acids like omega-3 and omega-6 and Linoleic acid are often added to the diet of dogs recovering from skin problems to help their skin heal. Vitamins C and E are also often found in dog foods for skin health.

What's a food intolerance?

Lots of people think their dog has a food allergy when what he really has is a food intolerance. So, what's the difference? Food allergies are true allergies. They cause itching and scratching and all the symptoms described above. A food intolerance is a gastrointestinal problem. Have you ever eaten something – maybe a food that you love – but it does a number on your stomach? Maybe you love spicy food but you spend the rest of the night in the bathroom. That's a food intolerance. Diarrhea and vomiting are symptoms of a food intolerance.

If your dog has a food intolerance, you will need to avoid feeding foods that contain that certain ingredient or combination of ingredients, just as you avoid foods for a food allergy. If you're not sure what the ingredient might be that's causing your dog's food intolerance, talk to your vet. She can work with you and your dog to identify the offending ingredient.

Does the quality of the food matter?

Nope. (Meaning - as far as allergies are concerned) Food quality has nothing to do with food allergies or food intolerances. You can feed your dog the best, most expensive organic/free range/pasture-raised dog food on earth but if it happens to contain something he's allergic to, he will have the same reaction. There is absolutely no reason for you to feel guilty for your dog's food allergy or food intolerance or feel guilty about what you're feeding your dog. This reaction is something your dog's body is doing. It's not something that you've done.

You should also know that food allergies and food intolerances can happen with any dog, male or female, spayed/neutered or intact, at any age (once they're no longer a very young puppy). Allergies and intolerances can suddenly develop even when a dog is much older. They happen to mutts and purebreds both. They just happen.

Carlotta is a writer for DogFood.Guru. She's a long-time contributing editor for the weekly dog show magazine Dog News. She's also the author of The Dog Adoption Bible, the Dog Writers Association of America Adoptashelter.com Award winner for 2013.

Thank you Carlotta for this great article.  When Oscar shows signs of being itchy, we call him Scratchy Von Itchy or Mr. Licky Pants.