Cat Food Allergies: Common Causes and Treatments

Whether your cat has made a mess in the litter box or is constantly scratching her own skin, any sign of discomfort in a beloved pet is alarming. Cats can’t tell us why they don’t feel well, and worse, they are skilled at hiding their illness until it becomes severe. 

If your cat is itchy and has diarrhea or other unpleasant gastrointestinal symptoms, a dietary problem could be to blame. Let’s explore whether certain foods can cause allergies in cats and if so, how you can help provide relief for your pet.

Can Cats Have Allergies to Food?

Yes, cats can be allergic to ingredients in their food. However, these food allergies are actually rare in cats. They are much more likely to have allergies to things in their environment, such as mold and grasses. When cats do have food allergies, they are typically directed at a specific protein source. Chicken is the most common food allergen in cats, but they can also be allergic to beef, turkey, egg, soy, or milk, as well as less common meat sources such as venison or duck. 

Cats are very unlikely to be allergic to grains or gluten. In fact, although cats are carnivores, grain-free or gluten-free foods are no more healthy for them than foods with grains and gluten. Most cat foods contain carbohydrates, such as wheat, corn, or potato, because they are an important source of vitamins and minerals. The total amount of carbohydrates in the food is a much more useful metric of healthfulness than whether it is grain-free. This is because foods higher in total carbohydrate content are associated with weight gain in cats.

What Causes Cat Food Allergies?

We don’t really know why food allergies exist. But we do know what happens in the body when a cat has allergies. Allergies occur when the immune system mistakenly identifies a protein from a food as a cause for alarm instead of a benign source of nutrition. This causes the cat’s body to mount an immune response, attacking the “invader.” Immune responses cause inflammation, and it is this inflammation that we see as allergy symptoms, such as itching (inflammation of the skin) and diarrhea (inflammation of the intestines).

Cat food allergies usually emerge in young cats but they can develop at any time in a cat’s life. Allergies may also get worse over time. Neither sex nor breed are specific risk factors, although there is early evidence that Siamese cats and their cross-breeds may have increased risk (1). About 25 percent of cats who have a food allergy also have an environmental or flea allergy (2).

Cat Food Allergy Symptoms

Unfortunately, cat food allergy symptoms are common to many other conditions and can vary widely between cats.

When humans have allergies to something in the environment, such as grass or pollen, they may cough and sneeze. While cats with environmental allergies can have respiratory signs, they frequently will lick their feet and bellies. Cats with environmental allergies may also develop ear infections. Some veterinarians also believe that feline acne is also associated with allergies. Feline acne occurs on the chin and has various appearances, from black dirt to zits to swelling of the whole chin area. 

To make things complicated, cat food allergies can also cause excessive licking and ear infections just like environmental allergies. But typically, food allergic cats will also have gastrointestinal signs, such as vomiting, diarrhea, or decreased appetite. Unfortunately, there is no specific set of cat food allergy symptoms. The gastrointestinal signs of cat food allergies are common to many other ailments in cats, including most types of gastrointestinal disease (parasites, inflammatory bowel disease, cancer, etc.), pancreatitis, liver disease, kidney disease, thyroid disease, and others. Although many people think it is normal for cats to vomit occasionally, in fact this could be the first sign that your cat has an allergy or other problem. Therefore, if you notice any of these signs, it is important to have your cat examined by a veterinarian. 

Signs of food allergies in cats can include:

• Licking feet, face, or abdomen
• Vomiting
• Loose stool or diarrhea
• Decreased appetite
• Weight loss
• Ear infection
• Excessive gas
• Miliary dermatitis (crusty bumps all over the cat’s body)
• Breathing problems (rare)

Diagnosing Cat Food Allergies

The best way to diagnose a food allergy in a cat is through an elimination diet trial. The idea is that if you can completely exclude the source of allergen from your pet’s environment, then the symptoms should resolve. 

Importantly, since the signs of food allergy are common to other diseases in cats, your veterinarian is likely to start with testing for and treating other more common causes of your cat’s symptoms. These include various causes of gastrointestinal inflammation, flea allergy, and environmental allergy. Once these causes of your cat’s symptoms are excluded, then it is time to start a diet trial. While any veterinarian can conduct a food trial, veterinary dermatologists are specialists who focus on skin and allergies and are often the best resources for diagnosing and treating allergic disease.

Although it sounds simple, an elimination diet trial is difficult to do properly. First, your veterinarian will select a novel protein or hydrolyzed food. Hydrolyzed means that the protein source in the food has been broken down into short chains of amino acids. (Amino acids are the building blocks of proteins. Proteins can be thousands of amino acids long.) These short chains are not recognized by the body as containing an allergen. For some cats, a novel protein diet is also an appropriate choice for an elimination diet. Novel proteins are those your cat has never been exposed to, such as venison, rabbit, or kangaroo. However, some foods may cross-react, such as chicken and turkey or beef and bison, and therefore diets with similar proteins may not be appropriate as novel diets.

Selection of the food is the easy part. The hard part is remembering to not give your cat any treats, snacks, medications, or supplements that contain anything edible other than the elimination diet. This means other cats in the house will need to be fed separately or else everyone needs to be on the same elimination diet. If you accidentally allow your cat to eat anything other than the prescribed diet, you have to start the whole trial timeline over again.  

Diet trials last from 4-12 weeks. Every 2-4 weeks, your cat will be evaluated by your veterinarian and you will discuss how she is doing. It is important for you to keep a record of her symptoms at home. The reason that diet trials have a broad timeline is that some cats respond to their elimination diet quickly, while for others it takes more time. An elimination diet trial is not considered over until your cat improves OR at least 12 weeks have passed without improvement. If a cat responds, gastrointestinal signs will usually improve before skin signs. This is because cells turn over more quickly in the GI tract than they do in the skin.

According to recent research, “alternative tests of blood, serum, saliva and hair have been found to be unsatisfactory” in the diagnosis of food allergy in cats (3).

How to Treat Cat Food Allergies

The best treatment for cat food allergies is to eliminate the allergen from your cat’s environment completely. This means that none of the ingredients in your cat’s food can come from the source of your animal’s allergy. These are usually called “limited ingredient” or “novel protein” diets. 

But more than just looking at primary ingredients, an allergen-free diet means there should be no risk of contamination with the allergen. It is similar to how some human foods that don’t contain peanuts are made in facilities that also process peanuts, so are not safe for those with peanut allergies. Human food is required to state any possible allergen contamination on the box, but there is no such requirement for cat food. In fact, very few pet food companies can guarantee no contamination. It is expensive to completely shut down machinery and deep clean it between making different foods, and most food companies are not designing food to be truly therapeutic. The few companies that do make this guarantee for their limited-ingredient diets include Royal Canin, Hill’s, and Purina. These guaranteed diets are usually the prescription diets, so they can specifically be labeled as a therapy or treatment for your cat’s disease (allergies). If you want to use a different brand of food for your cat’s allergen-free food, talk to your veterinarian.

In addition to allergen-free food, all treats, dental chews, medications, and toys should be allergen-free. It is okay for you to eat the food your cat is allergic to, as long as you don’t give her table scraps or let her lick the dishes.

Medication is unlikely to be required for food allergies in cats as long as your cat is maintained on an allergen-free diet. However, if a flare-up of symptoms happens, then your veterinarian may prescribe a short course of medication to get her feeling better faster.

Food allergy is just one of the many causes of your cat’s itchy skin or GI discomfort, and in fact one of the less common ones. Therefore, it is important to have your cat seen by your veterinarian before you change her diet or try to do an elimination diet on your own.