Environmental Allergies (Atopic Dermatitis) in Pets

Hey Furrends,

Rebecca at ATC Pet Talk here!

I want to spend some time going over atopic dermatitis or you may know it as environmental allergies. I have been working on completing my continuing education requirements to renew my veterinary technician license and I took a 2-hour course online about atopic dermatitis. I learned A LOT of valuable information during these lectures and thought it would be great to share it with you as this is an all around frustrating condition for owners, pets and veterinary professionals! 


  1. Diagnosis of exclusion
  2. Symptoms present differently from patient to patient
  3. It’s requires LIFELONG treatment and flare-ups are not uncommon

Ask my 7-year old domestic shorthair Athena and she will tell you how frustrating of a process it has been to diagnose and treat her atopic dermatitis. Athena’s case is quite interesting and I will expand on this in a little. For now, I just want to get across how frustrating atopic dermatitis really is and if you find yourself feeling this way just know that you are not alone, I understand your frustration and validate your feelings. 

Not only is atopic dermatitis frustrating, but it is also one of the most common skin conditions seen in dogs and cats!

What is Atopic Dermatitis?

Well, atopic dermatitis is the physical presentation of atopy or environmental allergies. I like to explain allergies as the body’s exaggerated immune response to an otherwise harmless substance. Our immune system is quite fascinating and essential for our survival. Similarly to other body systems, the immune system can develop abnormalities. These abnormalities manifest as allergic disease, immunodeficiencies and autoimmune disorders. The immune system is a complex network of cells and proteins that work together to defend the body against foreign invaders (bacteria, fungi, viruses, parasites). 

When a seemingly harmless substance, such as pollen or mold is absorbed deep within the epidermis, the allergen, a foreign substance, is accessible to the immune system. The allergen is captured by antigen-presenting cells and is carried to the lymph nodes where it is introduced to naive T lymphocytes. Naive T lymphocytes become activated and develop into T lymphocytes which produce a series of cytokines that instruct B lymphocytes to make Immunoglobulin E (IgE) initiating an allergic response. The IgE binds to mast cells in the skin where they remain waiting for exposure to the allergens. The mast cells will capture the allergens and signal the T cells at the site and activate a quick allergic response. The cytokine, interleukin-31, is released to bind directly to nerves to stimulate itch rapidly. Scratching and chronic inflammation causes the skin to thicken, an increase in nerve fibers and the development of secondary infections. 

We have learned that atopic dermatitis occurs because there is a skin barrier defect, which contributes to disease by permitting absorption of allergens more deeply into the epidermis, where the immune system can access them. Severity of atopic dermatitis is likely dictated by the number of allergic genes a dog inherits, the severity of the skin barrier defect, and the environment in which the dog lives. We now know that dogs absorb most of their allergens through the skin, and this absorption explains why we see the lesions where we do: in sparsely haired areas such as the feet, the periocular and perioral areas, and the ventrum.

Valerie A. Fadok, DVM, PhD, DACVD

Environmental allergens in dogs and cats are very similar to humans. Pets can have allergies to pollen, dust house mites, storage mites, mold, trees, weeds, grasses and fleas. Environmental allergies can either be seasonal or nonseasonal, however allergies that start as seasonal typically develop into year round occurrence. Pollen and fleas are more common in the warmer months. Fleas reproduce, hatch and mature much faster in the warmer weather. Research suggests multiple breeds are predisposed to atopic dermatitis, however, their genetic pool and geographic region are significant contributing factors. Dog breeds genetically predisposed to allergies include: Chinese Shar-Peis, Wirehaired Fox Terriers, Golden Retrievers, Dalmatians, Boxers, Boston Terriers, Labrador Retrievers, Lhasa Apsos, Scottish Terriers, Shih Tzus, and West Highland White Terriers. Age of onset is usually 6 months to 3 years old. In cats, allergies are more common in purebreds than domestic short hairs. Age of onset differs from case to case but allergies usually present before 5 years of age.

Red, irritated skin

Pruritus is the characteristic sign of atopic dermatitis.

Sandra Diaz , DVM, MS, DACVD

Clinical Symptoms of Atopic Dermatitis

Itching is the most common sign of allergies in dogs and cats. Skin irritation usually appears on the paws and ears in dogs, however, it also occurs on the feet, face, front legs, underarms, abdomen, and groin. Interestingly, primary lesions or lesions caused as a direct result of environmental allergies are rare while secondary lesions are very common. When a pet repeatedly scratches, bites and licks their skin, they are more likely to break the skin resulting in an increased risk of developing bacterial and yeast infections. Secondary lesions are lesions that result from repeated self-trauma and include: alopecia (hair loss), erythema (redness), crusts and scales, lichenification (thickened, leathery skin) and hyperpigmentation (darkening of the skin). Only 15% of dogs and cats with atopic dermatitis will experience rhinitis and asthma. Additionally, a small portion of pets with atopic dermatitis experience chronic or recurrent ear inflammation without any other skin-related issues.

Diagnosis and Treatment of Atopic Dermatitis

The 2-hour CE lecture presented by Dr. Phil Thompson and Dr. Candace A. Sousa talked a lot about the process of diagnosing canine atopic dermatitis and stopping the itch. They both agreed to rule out the more easily treated causes of itch as a process of elimination before jumping to atopic dermatitis. The first pathologies to investigate are parasites, including fleas, scabies and demodex and then primary bacterial and fungal skin infections, underlying systemic disease (hypothyroidism), potential food allergies and finally atopic dermatitis. Diagnosis also relies on breed, age, signs and disease history (i.e. age when the symptoms first appeared). Specific tests for atopic dermatitis are performed once all the other pathologies have been ruled out. There is no specific test for allergies, instead tests are used to detect allergens. Definitive diagnosis of atopic dermatitis is either supported through ELISA tests or for allergen specific IgE or through intradermal skin testing. 

They both agreed that steroids are effective at treating the itch, however, they rarely utilize them because there are safer long term options without as many serious side effects. They both agreed that Aopquel and Cytopoint are their “go to” treatments for controlling itchiness. Apoquel is an interleukin-2 inhibitor and Ctypopoint is a monoclonal antibody that targets interleukin-31. Apoquel and Cytopoint are only used for dogs, however, Apoquel can be used off label for cats. Atopica is an immunomodulatory drug which inhibits the immune response to an allergen. This drug interrupts the immune response responsible for an allergic reaction instead of just treating the itch like Apoquel and Cytopoint. Atopica is safe to treat atopic dermatitis in both dogs and cats. 

Steroid Use in Cats

Steroids are safer in cats with fewer long term side effects compared to dogs. However, cats still  need to be monitored for potential side effects. The dose needs to be tapered over time to the lowest effective dose. Long term use of injectable steroids can cause cardiac issues and should be avoided which has been observed in 11% of cats. Diabetes and urinary tract infections have also been observed. 

Histamines are not considered an effective medication for treating the itch caused by allergies, however they are effective at controlling ear inflammation resulting from allergies. This is because histamine, which antihistamines target are involved in the inflammatory process. Antihistamines have proven to be effective for my cat, Athena.

“Recently, a randomized, double-blind, placebo controlled, cross-over clinical trial was performed to assess the efficacy of cetirizine administered orally at the dosage of 1mg/kg in cats with allergic dermatitis” (Wildermuth et al., 2013). This study found no significant difference between treatment and placebo.” Antihistamines are worth trying because they are inexpensive and have few side effects. In combination with fatty acid supplements, antihistamines help 10-25% of pets with atopic dermatitis.

Pros and Cons to Cytopoint, Atopica and Apoquel

Atopica (cyclosporine)

  • Takes 5 to 7 days to work
  • Immunomodulatory drug, cyclosporine: an alternative to steroids
  • Inhibits immune response to allergen
  • Targets the cause of itchiness
  • Treats the cause and helps prevent infections
  • Good for pets with inflammatory disease and infections
  • Can be used for cats
  • Possible side effects: nausea , vomiting, diarrhea, loss of appetite
  • Is safe and well tolerated esp. for cats resistant to glucocorticoids or who are diabetic

Apoquel (oclacitinib)

  • Inhibits the nerve response, inhibits the function of a variety of pruritogenic cytokines and pro-inflammatory cytokines
  • Begins to work the same day its given
  • Decreases the itch
  • For flare ups, covers up the issue (abnormal immune response)
  • Dosing: 1 tablet twice a day for 2 weeks followed by 1 tablet for the remaining course 
  • Owners can use this if Cytopoint begins to be ineffective 
  • Not FDA approved for use in cats, however, it can be used off-label if owner consents as side effects are unknown in cats
  • Shouldn’t be used in dogs with serious infections, such as parasitic infections or with cancer patients or patients with a history of neoplasia
  • Most common side effects: vomiting and diarrhea
  • Less common side effects: pyoderma, non-specified dermal lumps, otitis, histiocytoma, cystitis, anorexia, lethargy, yeast skin infections, pododermatitis, polydipsia, lymphadenopathy, lipoma, nausea, and aggression


  • An injection that begins to work the same day it is administered and is effective for 4 to 8 weeks 
  • Monoclonal dog antibody that blocks itch signal to nerve, targets cytokine interleukin 31
  • Decreases the itch
  • Relief from chronic itching, but covers up the issue (abnormal immune response)
  • If administered when the seasons are changing it can prevent itchiness for four months because the pollens aren’t as bad by the time it wears off
  • Not used in cats
  • No side effects of concern since biologic, one study reported mild vomiting, diarrhea and lethargy

Allergen Immunotherapy

Immunotherapy is the only treatment option that has the potential to prevent lifelong flares, however, most require lifelong administration. Studies suggest that 60% to 80% of atopic dogs and cats benefit from immunotherapy, however it can take up to 6 months to 1 year to notice results. The goal of immunotherapy is to alleviate the itch by desensitizing the body to allergens. The allergy serum can be formulated for subcutaneous injection administration or oral transmucosal drops. A dosing schedule is created to provide a controlled stimulation of the immune system via exposure to allergens, which the patient will develop a tolerance to overtime. The concentration of allergens slowly increases but is low enough to rarely cause an allergic reaction. The most common allergic reaction is a minor localized skin reaction, however, an anaphylactic reaction is possible but is extremely rare. Pets should be observed for 60 to 90 minutes after administration for adverse reactions. Therefore, one of the veterinary professionals will go over the symptoms of anaphylaxis with you just to be safe. 

Diagnosis and immunotherapy treatment is performed by a board certified veterinary dermatologist and is expensive. There is no actual way to test for allergies, instead there are tests that determine what specific allergens cause a reaction. Diagnosis is also based on breed, age, symptoms and history (i.e. age when the symptoms first appeared, etc.). In rare circumstances, allergic symptoms may worsen. If this happens contact your dermatologist. Also, talk to your vet if symptoms return, change or do not improve with therapy. It’s important to be patient and follow the specific instructions.

Heska Allercept Testing and Intradermal Testing

The Heska test measures allergen-specific Immunoglobulin E (IgE) antibodies in a blood serum sample. The Heska test rarely produces false positives, but is more likely to produce a false negative compared to intradermal testing. Intradermal testing is performed by a board certified dermatologist. The patient needs to be fasted and sedated for the procedure. A grid will be drawn on the abdomen once shaved. Tiny injections of 48 different environmental allergens are injected into each square, including: house dust, house dust mites, trees/grasses/weeds pollens, insects, fleas and molds. After ~ 20 mins, redness and raised circular lesions will appear in the squares that induced an allergic reaction. If allergies are seasonal it is best to schedule testing during August to November. Prior to intradermal testing, certain medications including steroids and antihistamines need to be stopped for a specified period of time, however the Heska test does not require discontinuation of medications. If the Heska test comes back positive for allergies, no further diagnostic testing is required. However, if the Heska test comes back negative and the patient’s history and clinical symptoms strongly suggest environmental allergies, the dermatologist may recommend intradermal testing. 

Intradermal Testing
Intradermal Testing
Heska Allercept Testing

Remember, there is no cure for allergies, but they can be controlled through various methods:

  • Avoidance of allergens
  • Controlling the itch and flare ups with medications
  • Regular bathing and grooming, topical anti-itch shampoos
  • Immunotherapy (allergy shots)

Subcutaneous Injections

  • Keep serum vial refrigerated 
  • Warm serum, either in bottle or syringe
  • Gently invert serum vial several times and wipe the rubber top with an alcohol pad before drawing up syringe 
  • Use a new syringe and needle for each injection
  • The volume of serum will gradually increase over the induction period of several weeks 
  • Hold bottle upside down and pull back on plunger to the appropriate volume 
  • Gently flick the syringe to expel air bubbles 
  • With one hand, tent the skin (create a triangle or “U” shape) between the shoulder blades “the scruff area”
  • Insert the needle, draw back on the plunger to check for blood. If no blood it noticed, push down on the plunger to administer the injection. If blood is noticed, redirect your syringe.
  • If your pet suddenly moves and the full volume of serum is not administered (you’ll notice as the fur will be wet), do not readminister. Instead call your dermatologist for further instruction
Tenting the Skin Technique
Tenting the Skin Technique

Ah-Ha! Finally, I am going to talk about my personal experience regarding my cat, Athena, who suffers from atopic dermatitis.

The story begins in August of 2019. I came home from work and noticed that something was off with Athena. She was acting abnormal (which is a common sign of pain and discomfort). Athena is a super cuddly and friendly cat who will follow you around the house and jump on top of you when you are sitting or laying down. Athena did not greet me at the door like she usually does. I went over to her cat tree and picked her up. She immediately jumped out of my arms. I decided to do my own little physical exam and scan her body for obvious signs of abnormalities. I noticed a tiny scab on the pinna of her left ear. I palpated the base of the ear and noticed a white milky discharge. I took her to her GP veterinarian the next day. During the night, Athena’s symptoms worsened. She had developed Horner’s Syndrome which is an eye abnormality caused by nerve damage. The nerve damage prevented sympathetic nerve innervation to her left eye. As a result, she experienced pupil constriction, eyelid drooping, prolapse of her third eyelid and her eyeball was sunken back into her orbit (see image below).  The veterinarian performed an in-house cytology which came back positive for Streptococcus species of bacteria. The veterinarian sent me home with antibiotics, anti-inflammatories, ear flush and lubricating eye drops.

Horner's Syndrome

I took her home and started her medications. At around 2am, I woke up as Athena was in the bed flopping around. She was unable to balance, stand up or walk without falling over, she developed nystagmus (involuntary repetitive eye movements) and was open mouth breathing. As a veterinary technologist, one of the first things we learn in our program is that open mouth breathing in cats is a sign of an emergency. Luckily, I was living at home at the time and was able to wake up my dad to drive us to the emergency clinic as it was not safe for me to drive in that state. Since I was working in the ophthalmology department at the specialty clinic, I was able to take Athena into the back of the clinic to see a critical care veterinarian. She told me not to worry as this has happened to one of her cats who had an ear infection and while it had appeared extremely concerning and does cause her discomfort she was not in critical condition. The veterinarian took radiographs of her lungs just to put my mind at ease. Her lungs looked exceptional. She then prescribed Athena additional antibiotics for gram negative bacteria, anti-nausea medications and a sedative to help her relax. I took her home and continued her on her medications for several weeks. At this time, she had to remain in a crate as she posed a danger to herself. I turned one of my big dog crates into a temporary home for Athena. She was unable to eat dry food for several weeks. In the beginning, I would hand feed her wet food and eventually she would eat on her own. After several weeks, I introduced dry food back into her diet. She seemed to be doing well. She was able to stand up and move around, her Horner’s Syndrome improved and her nystagmus resolved. I began letting her out of her crate.

Nystagmus, Vestibular Dysfunction and Open Mouth Breathing

Whooohooo! but, not really...

Athena’s symptoms began to return and I spoke with a specialty veterinarian who recommended she be put on a long course of antibiotics. At the end of the 6 weeks, she seemed to be doing a lot better, but within a couple weeks her symptoms had returned. Her tympanic membrane “eardrum” was ruptured, which could not be diagnosed until the discharge had subsided. I scheduled an appointment to meet with the neurologist. She recommended having a CT scan performed to see if there was a polyp or tumor in her bulla space. The CT scan showed an abnormality in her bulla space. You can see from the image below that her right bulla space appears black meaning that it is filled with air, which is normal while her left bulla space appeared white on imaging. I decided to schedule a consultation with the internal medicine specialist to get advice on what to do going forward. After discussing the options, I decided to schedule Athena for a ventral bulla osteotomy, a surgery that involves making an incision in the neck allowing access to the bulla space. It turns out there was no tumor or polyp, but she did have discharge. Her surgeon cleaned out the discharge and debrided the tissue to encourage healing. The results after her surgery seemed promising. However, within a week or so she was not acting normal and I noticed more discharge in her ear. I took her back to the internal medicine specialist who referred me to a board certified dermatologist. 

Athena's CT Scan

The dermatologist performed an inhouse cytology. Her ear canal was full of yeast, which makes sense since she was on antibiotics for a long time. She sent me home with a course of steroids and antifungal medication. After recurring flare ups every couple weeks, more steroids, antifungal medication, and antihistamines we decided to check for environmental allergies. A blood sample was drawn and sent out for a Heska test to look for antibodies to common allergens. Luckily, it came back positive. I say lucky because after all this time, we had finally found the source of her recurring ear inflammation and infections. The main allergens of concern were dust and storage mites. I decided I wanted to start her on immunotherapy. I started her on her loading dose schedule, which I have provided below and continued her on antihistamines. Athena had her last recheck about 1 month ago and her ear looked amazing. 

She did and continues to have a left-sided head tilt. Prior to starting her on immunotherapy, she would meet with a chiropractor once a month to attempt to correct it. Unfortunately, there was little improvement seen and her head tilt remains static. However, it does not seem to bother her. She is able to walk, run and jump perfectly normal. 

Athena is currently on her maintenance dose, which is 1mL of vial #2 every two weeks. Her next recheck appointment is in February and I will make sure to let you all know how she’s doing! Thank you for your love and support! Athena is one strong, resilient kitty. She has yet to bite or scratch me when administering her pills and injections and she has remained loving and affectionate to me throughout this entire time! 

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