Mercer Island Veterinary Clinic
2448 76th Ave SE Suite 102 | Mercer Island, WA 98040

(206) 232-0333

info@mercerislandvet.com
M-S 7:30am-6pm, Sun Closed



Why is my dog or cat itchy? An overview of skin allergies in dogs and cats.

Is your dog or cat keeping you up at night scratching. licking or chewing? As spring approaches, itching and allergies are a common complaint among our clients.

The first step when ANY pet (cat, dog, indoor, outdoor) begins itching is to consider fleas. Even if a pet is mostly indoors, humans can track in fleas on our clothing or shoes. Certainly checking your pet for fleas – look toward the back half of the pet, around the tail, or on the belly – is a helpful exercise. However, even if you don’t see fleas, remember that a single bite can cause a pet to become itchy all over. This is because of flea allergy dermatitis, which can vary in severity from mild to quite severe. These pets are allergic to flea saliva, so when a flea bites (even if it doesn’t take up residence) it can cause a systemic allergic reaction causing a pet to be itchy for days to come. We do recommend year round flea control for all pets in the Pacific Northwest, as it is typically not cold enough to kill fleas in the winter due to our temperate climate. We see cases of fleas all year at Mercer Island Veterinary Clinic. Give us a call if you are concerned about fleas and we can help guide you to the proper preventative medication for your pet. We do not recommend applying over the counter flea medication to your pet, especially cats, without consulting with the veterinarian first. Also remember that if you do find fleas, what is seen on the pet is only 5% of the problem. The other 95% is in your environment – carpets, baseboards, rugs, furniture, where the immature larval stages will lay dormant for weeks to come. For this reason, treating the environment is also vitally important. We can guide you through the best products and techniques to clean the environment of fleas safely for all family members.
If the itchiness is not resolved after fleas have been addressed, it is time to come to a veterinarian for further workup. If skin allergies are suspected as the underlying cause of itchiness, red skin, bumps, or crusting there are two main goals of treatment. The first is to diagnose and treat any secondary infection that is present. A sampling of your pet’s skin using a tape cytology, skin scraping or cultures may be utilized to direct treatment specifically, or combination products may be utilized to treat common pathogens. Depending on the severity of disease, topical and systemic products are used to target the bacterial and fungal species that commonly overgrow on the skin of allergic patients. This occurs because of the underlying inflammation which alters the skin’s immune system “barrier function” and makes the skin more susceptible to infection. Pets that chew, scratch and lick also disturb the top layer of the skin that helps to resist infection and exacerbate the problem. It is important to treat secondary infection, as it will contribute to the itchiness and inflammation that your pet experiences.
The second goal of therapy is to address the underlying cause of the allergy, and reduce the resultant inflammation and pruritis (itch). There are several underlying causes of skin allergy in dogs and cats, and often pets can have components of each that contribute to their disease.  As described above, the first is flea allergy dermatitis. This is an allergy to flea saliva, so that when a pet receives a flea bite, it incites a systemic inflammatory reaction. This can be a problem even if there are no fleas found on the pet, as it takes only the bite of the flea to trigger the allergy.
Another cause of itchiness is a food allergy. This is typically to the protein in the diet such as beef, chicken, pork, or fish. To rule out a food allergy we perform a diet trial with a veterinary hypoallergenic diet such as Hills D/D. This food has a single protein and starch as well as added omega 3 fatty acids which boost the skin’s immune system. A veterinary diet is recommended because care is taken in production to make each flavor in a separate bin so there is no cross-contamination between proteins. Over the counter hypoallergenic diets (even expensive foods from the pet store) have been found to have traces of allergenic proteins such as beef or pork. A diet trial involves feeding the food exclusively for 8 weeks at the minimum before assessing results. Ideally, the protein chosen would be one that your pet has not been fed previously.  We often start by eliminating food and flea allergy, as these are more readily treated and do not require administering systemic medications. In addition, if a pet has a small component of each type of allergy, we may be able to significantly reduce symptoms by just providing religious flea control and the correct diet.

The final trigger of skin allergy in pets is the most common – environmental allergies. These comprise 85% of allergies in dogs and cats. Environmental allergens include grasses, pollens, trees, dust mites, or molds. This is disease is called atopic dermatitis (atopy). We can test for environmental allergy by submitting bloodwork to screen for antibodies to certain common allergy triggers. In other cases, we may refer you to the dermatologist for intradermal patch testing against common allergy triggers. As avoidance of these types of allergens is nearly impossible, we use other methods to treat this disease. The results of allergy testing can be used to formulate injections or oral medication (allergen specific immunotherapy), which over a period of time allows us to desensitize your pet to the environmental allergens that he or she is sensitive to. Successful therapy can lead to decreased severity of disease, which translates to fewer medications and treatments for your pet. Allergen specific immunotherapy is helpful for 60-70% of pets. Alternatively, symptomatic therapy with immune modulating medications such as anti-inflammatory steroids or the new anti-itch drug Apoquel can be used to temporarily relieve inflammation secondary to atopy. Other pets require a small amount of these medications in addition to the allergy injections for long term maintenance. Similarly, antihistamine medications are utilized to decrease histamine release which is an important mediator of itch. Finally, bathing is an important part of an atopic pet’s maintenance routine to reduce the number of allergens that have prolonged contact with the skin.
If your pet is the appropriate age or breed we may consider testing for hormonal diseases such as hyperadrenocorticism or hypothyroidism which can also trigger skin disease, and mimic allergic skin disease as described above.
I hope this finds you and your pet families well as we head into the spring season. As always, we are here for you and your pets, do not hesitate to call or email with questions.

Take care,
Julia Mulvaney, DVM