Atopic Dermatitis (Atopy) in Dogs

What is atopic dermatitis?

Atopic dermatitis (atopy) is a common skin condition in dogs characterized by itchy, inflamed skin. It occurs when a dog encounters an environmental protein to which it is allergic (an allergen), which sets off an immune reaction that leads to skin problems. While the incidence of atopy is hard to define due to challenges in diagnosis, approximately 10%–15% of dogs treated by veterinary dermatologists are diagnosed with atopy.

What causes atopy?

Dogs with atopy are often allergic to the same allergens that tend to affect humans: tree pollen, grass pollen, weeds, molds, and dust mites. While these allergens cause watery eyes and a runny nose in humans, dogs respond differently and often develop skin inflammation in response to these allergens.

Underlying defects in the skin barrier can make individuals predisposed. Certain dog breeds are more prone to atopy, including boxers, English bulldogs, cocker spaniels, French bulldogs, fox terriers, German shepherds, golden retrievers, Irish setters, Labrador retrievers, poodles and poodle crosses, shar peis, vizslas, and West Highland white terriers. Symptoms typically start when the dog is between 2 years and 6 years of age.

What are the signs of atopy?

Affected dogs often have a history of chronic or recurrent itching, which may be seasonal or non-seasonal. Dogs with atopy also tend to have a history of recurring skin and/or ear infections. Chronic infection of the ears or skin can lead to dark, thickened, elephant-like skin. In many cases, affected dogs are so itchy that they create significant trauma to their skin. Affected dogs may have severe scratches or abrasions, reddish-brown saliva staining in itchy areas, and red skin due to chronic licking and inflammation.

How is atopy diagnosed?

Your veterinarian will begin with a thorough physical examination of your dog. Your veterinarian will also take a complete patient history, asking you a variety of questions about your dog’s skin disease to better characterize the condition. From the physical exam and history, your veterinarian may begin to suspect atopy as the cause of your dog’s skin disease.

Unfortunately, there is no definitive test for atopy. It is a diagnosis of exclusion, which means your veterinarian will rule out other, similar skin conditions to arrive at a diagnosis. The signs of atopy are identical to many other skin diseases. 

• Your veterinarian will likely perform tests to rule out skin parasites (e.g., fleas, mites, lice), bacterial skin infections, and ringworm. 
• Your veterinarian may perform a biopsy to rule out autoimmune skin disease and other conditions. 
• Your veterinarian may also recommend a food trial to rule out food allergies as a source of your dog’s skin issues.

Your veterinarian may also perform tests to assess your dog’s overall health. These tests will help rule out underlying medical conditions and determine whether your dog can be safely treated with medication. Laboratory tests may include a complete blood cell count (CBC), serum biochemical profile, T4 (thyroid test), and urinalysis.

Certain other tests can help guide the management of atopic dermatitis:

• Intradermal allergy testing. This test involves injecting very small amounts of many different allergens into your dog’s skin and monitoring your dog’s immune response to these substances. This test can help determine which allergens your cat reacts to most strongly, which can help guide treatment.
• Serologic allergy testing. Like intradermal testing, serologic allergy testing aims to determine which allergens are triggering your dog’s allergies. This test is performed on your dog’s blood. Serologic testing is generally considered less reliable than intradermal testing; however, it is often less expensive and does not require sedation, making it a viable option in some cases.

How is atopy treated?

There is no single best treatment for managing atopy in dogs. Allergies are managed, not cured, and the best method varies depending on the patient and owner.

Anti-inflammatory drugs often bring relief from itching, including, corticosteroids (e.g., prednisone) and cyclosporine (Atopica®). Antihistamines are also tried sometimes, although they appear to be relatively ineffective for dogs that are already suffering from itchiness.

 Newer therapies include oclacitinib (Apoquel®) and ilunocitinib (Zenrelia®), which are medications that inhibit some of the chemicals released within the skin thatt contribute to inflammation and itch. Lokivetmab (Cytopoint®) is another medication that is given by injection every 1–2 months. It is an antibody that blocks interleukin-31, which is a protein that transmits itch signals. These newer medications control itch without the potential side effects of using corticosteroids.

Certain omega fatty acids (omega 3 and 6) provide some relief for many pets with allergic skin disease by reducing inflammatory chemicals within the skin and improving the skin barrier. Antibiotics or antifungals may be required if there is a secondary bacterial or yeast skin infection present.

Atopic dogs may also benefit from allergen-specific immunotherapy (allergy shots). This treatment involves giving the dog injections or oral drops of very small amounts of substances they are allergic to (as determined by intradermal and/or serologic allergy testing) to build up their immune tolerance. This process takes time, and benefits are often not apparent until three to twelve months (or more) of treatment. These allergy injections result in significantly reduced itching in about half of dogs treated.

Many dogs benefit from frequent bathing with special shampoos, sprays, or mousses (topical therapy). Research shows that, because allergens are absorbed through the skin, frequent bathing may help reduce the amount of allergens that a dog absorbs. Some of the topical therapies incorporate omega fatty acids and ceramides, which may be absorbed into the skin, strengthening the skin barrier to help reduce the itching. Others will reduce the secondary overgrowth of yeast or bacteria on the skin that makes your dog itchier.

There may also be environmental measures you can take to decrease your dog’s exposure. For example, a dog that is allergic to dust mites may benefit from changes in household cleaning practices. Dogs allergic to food storage mites may benefit from a change from a dry diet to a canned, hypoallergenic diet, which will not contain these mites.

If your dog has a secondary skin or ear infection caused by allergies, this infection will also require treatment. Skin infections are often treated with oral or injectable antibiotics. Ear infections are usually treated with drops applied to the ears.

My dog has a grass allergy. Does that mean he should not walk on grass?

No, so-called grass allergies are more correctly termed grass pollen allergies. Pollens are airborne. Closely cut grass with no seeding heads will cause fewer problems for your dog, but there is little you can do to prevent your pet from being exposed to grass pollens.

Are there any other conditions connected with atopy?

Yes, some dogs with atopy also have hypothyroidism (low thyroid gland production). Hypothyroidism affects the skin and may worsen allergic skin conditions. Dogs with chronic skin infections or allergies should be tested for hypothyroidism. If your dog has hypothyroidism, desensitization therapy and anti-inflammatory medications will often fail to help your pet unless the hypothyroid condition is also treated.

When my dog’s allergies flare up, she seems to have a terrible smell. What causes this?

When allergies occur, the skin produces more sebum, which is an oily material that causes a musty odor. Once the itching and scratching are controlled, the odor and seborrhea should clear up. A skin or ear infection may also cause skin odor. Bacteria, and yeast are opportunists that can cause a secondary infection in dogs with underlying atopic dermatitis. The secondary infection may require specific antimicrobial treatment in addition to the allergy treatment.

What is the prognosis for atopy?

Unfortunately, the signs of atopy tend to worsen with age. Your dog will likely require lifelong treatment to manage atopy and the resulting secondary infections. Fortunately, there are a variety of medical treatments available for atopy, with new drugs constantly being developed. Therefore, it is typically possible for atopic dogs to have a good quality of life with ongoing care.