Environmental vs Food Allergies in Dogs, (Signs & Diagnosis)

Itchy dog? Is your dog keeping you up all night licking, chewing, or scratching? If you’re at your wits end seeing your dog miserable and itchy all the time, it’s likely that your dog is experiencing some type of allergic disease. Chronically itchy dogs get two types of allergies: environmental and food. How do you tell which one your dog has? Pinpointing the exact cause of their itchiness will bring your pooch some permanent relief.

Environmental allergies in canines

Like humans, dogs are also allergic to things in the environment (trees, weeds, grasses, molds, etc). Dogs with environmental allergies may be itchy only during certain seasons (usually spring, summer, and fall), but they may also be itchy year round. Most dogs start to become symptomatic around 2 years of age.

Signs of environmental allergies

  • Persistent or waxing/waning itchiness
  • Chronic bacterial/yeast skin infections (rashes, pustules, plaques, severe redness)
  • Paw licking
  • Recurring ear infections
  • Hair loss
  • Dry, flaky skin
  • Overly oily skin/coat
  • Dry, brittle, thin coat
  • Sneezing, coughing, or runny eyes (less common)

Diagnosing environmental allergies in dogs

Environmental allergies can be diagnosed in a couple of ways. Most dogs who are diagnosed at a later age can be given a diagnosis just based on their history of what seasons make them itchy. If your dog has been going to the vet every late summer and fall for hairloss and a rash on his belly, then it’s pretty clear they are allergic to something blooming around that time of year.

A diagnosis can also be made by presumptively treating for environmental allergies. Your vet can prescribe a (non-antihistamine) medication meant to control itch associated with allergies. Based on their response to these medications, it will confirm or deny environmental allergies. If your dog’s itchiness doesn’t improve on the medicine, then your doctor may be suspicious of a food allergy.

A definitive way to diagnose environmental allergies is with an allergy skin test performed by a veterinary dermatologist. Similar to human allergy tests, your veterinarian will inject common regional allergens under your dog’s skin and based on their superficial reaction to each individual injection, your veterinarian will determine what they’re allergic to.

Treating environmental allergies

There are a handful of ways to treat for environmental allergies, and thankfully veterinary pharmaceutical companies have gotten on board with better ways to treat allergies in canines.


The veterinary field used to believe that histamine played a big part in itch with dogs, but it’s recently been proven that it has very little to do with allergic itch. Histamine plays a role in severe allergic reactions, like insect stings, but in environmental allergies, it has very little to do with any itchiness.

However, if your dog has rhinitis symptoms (sneezing, coughing, runny nose/eyes), then a daily antihistamine can be helpful in treating those symptoms. Benedryl is usually the first choice, but dermatologists find dogs respond better to over the counter anthistamines like Zyrtec or Claritin.


Steroids are the oldest choice in medically treating allergies but the least preferred currently. Most dogs respond well to this drug in terms of relieving itchiness, but long-term use of steroids are contraindicated because of the negative effects it can have on the liver. Other side effects include increased thirst, urination, and hunger, as well as excessive panting and restlessness.

Immunomodulatory medications

The second oldest allergy medication is a drug called cyclosporine. In human medicine, it’s prescribed to organ transplant patients to prevent rejection after a transplant. When it’s prescribed for allergy dogs, it’s meant to quell their immune system’s overreaction to what they’re allergic to (as well as being used for a variety of immune-related disorders).

Unfortunately, it is expensive in large dogs, but side effects are limited to vomiting and diarrhea when the medication is first started. After that, there are no associated effects on organs when used long-term and is considered a very safe drug.

If your vet prescribes this for your dog, they will likely start them on a short course of oral steroids to help with any present itchiness as the cyclosporine can take 3-4 weeks to begin working.


Apoquel (oclactinib) is one of the newest drugs on the market. It targets a molecule called interleukin 31 that causes itchiness. The drug stops itchiness within 2 hours of taking it and lasts for 24 hours. Many dogs are able to stay well-controlled on this medicine and it drastically cuts down on flares and allergy-associated skin and ear infections when given consistently.

Apoquel is only available by prescription through your veterinarian, and there is no generic version available yet. It’s incredibly safe to use long-term in dogs over 1 year of age, and there are no side effects associated with Apoquel except some sleepiness the first few hours after administering.


Cytopoint (sometimes also known as canine atopic dermatitis injection [CADI]) is a monthly injection that works almost indentically to Apoquel. It simply neutralizes interleukin 31 which causes itch, preventing this molecule from reaching the brain and triggering itchiness.

It lasts 4-8 weeks (although most dogs only experience 4 weeks of relief before needing a repeat injection) and doesn’t cross any organs, so it’s safe for dogs of all ages, including dogs with liver or kidney disease. There are no reported side effects by the manufacturer either, so if your dog has a history of a sensitive stomach, this may be a great option for them!


If you opt for skin testing, your dermatologist will then initiate allergen immunotherapy. This is formulated from the results of the skin test. Small amounts of what they’re allergic to are put into an injectable or oral “vaccine” and administered biweekly (injection) or daily (oral), introducing controlled amounts of their specific allergens to gradually train their immune system to not overreact when they’re exposed to allergies. This therapy takes 12-18 months to work, but the 70-75% of dogs who respond favorably to this therapy are controlled only on their vaccine.

Food allergies in dogs

Food allergies are very common in dogs, especially purebred dogs like German shepherds, Labradors, and poodles. Unlike environmental allergies, you may note your dog was itchy as a puppy and it is gradually getting worse as they get older.

Unfortunately, dog food companies have capitalized on dogs being allergic to grains, but it’s actually very rare for dogs to be allergic to grain. Instead, they are almost always allergic to the protein source in their food, most commonly chicken or beef. In fact, there have been a handful of studies release showing dogs who are on grain-free diets long term can develop heart disease because of the lack of taurine in their diet.

Signs of a food allergies in dogs

  • Chronic, persistent itchiness that typically starts around 6 months of age, but may not be noticeable until around 2 years of age
  • Hair loss
  • Dry, brittle unhealthy coat
  • Chronically red, inflamed skin
  • Rashes
  • Chronic or frequent intermittent diarrhea
  • Recurring nausea
  • Ear infections

Testing for food allergies in dogs

Despite many companies advertising saliva, blood, or hair tests to test for food allergies, none of these are medically accurate. The veterinary field has been trying for years to develop an easy way to test for food allergies, but they have been unable to come up with anything.

Thus, the only true way to confirm or deny a food allergy is with a strict food trial using a prescription diet with a novel protein (a protein source your dog hasn’t been exposed to). A prescription diet is important because all foods are manufactured on equipment where other foods are made, meaning there is significant cross-contamination. A prescription food has strict quality control to prevent any cross-contamination.

Of the prescription diets, the commonly used protein sources are rabbit, kangaroo, or crocodile. When you begin the trial, your dog can only have this prescribed diet and nothing else for a full 8-12 weeks. Treats and human foods are off limits.

If your dog is no longer itchy at the end of the trial, it means they have a food allergy and will need to stay on this diet for life. If their itchiness gets better, then it could mean they have a food allergy on top of an environmental allergy.

Treating food allergies

There isn’t any way to treat a food allergy except to put them on a prescription food with a protein source they aren’t allergic to. This alone will keep your dog itch free.

Itchy dogs are often miserable dogs, so getting to the root of their itchiness is the best way to return your dog to their former state of happiness. The best way to get a diagnosis is to seek the medical care of a veterinary dermatologist because they specialize in treating allergies and can get to the bottom of the issue before it gets completely out of hand. The good news is allergies are very treatable and your dog can live a long, normal life!

Jackob Evans

Hi, I’m Jacob. I’ve been a professional blogger for over six years, and in that time, I’ve written countless blogs that have helped millions of people worldwide. A DVM by profession, I have treated and cured thousands of dogs, if not millions.

Leave a Comment