Allergic Dermatitis and Other Itchy Skin Conditions

by Bruce W. Little, DVM


This is the time of year across much of America when skin conditions on your pet can drive the entire household crazy with their constant licking, biting and scratching. The sound of thump, thump, thump in the middle of the night when your dog is scratching behind its ear with a hind leg is all too familiar and frustrating to most people who share a home with an itchy pet. I recall from my more than two decades of clinical veterinary practice the intense frustration of entire families bringing their dog or cat into the animal hospital because of incessant scratching, chewing and rubbing on their ears, paws, tail and any other part of their body they could reach. Many factors can enter into the reason pets develop skin conditions called dermatitis, and most of them trigger an alarm that prompts the pet owner to seek out a veterinarian. Whether it be due to the dry, dusty and less humid conditions as the summer heat burns itself out, the fall of the year seems to bring the most concern for dermatitis in our pets, although many skin problems can manifest themselves year around in most parts of the country.

It might come as a surprise, but there are over 160 skin conditions that affect dogs and cats. Some of these conditions are treatable and can be resolved with a successful cure of the itchy skin, while others are of a more chronic nature and have to be monitored and controlled with selected diets, medications, supplements, shampoos and other skin treatment products over a long period of time. Your veterinarian needs to gather a complete history of the symptoms that were observed leading up to the incessant scratching and biting of body parts. The part of the body the dog or cat scratches, licks and bites can be important in determining the cause of the itchy skin. Evidence of hair loss, redness, scales or scabs, or even open sores on the pet’s body are important. Has there been a change in the food over the past twelve months that the dog or cat eats? Has there been another pet come to the house or through the yard that may have transmitted parasites to your pet? All these items are important in the diagnosis and eventual treatment of the condition and need to be related to the veterinarian or his assistant. Sometimes the cause is relatively easy to diagnose, such as an ear infection caused by a fungus or mites that can be eliminated and treated quickly and effectively. Yet, other causes of dermatitis can be extremely difficult to both diagnose and treat, and can present a problem for the pet for a long time, and sometimes for the balance of the pet’s life.

Many ear infections are due to allergies that develop within the pets system. The ear canal with its warm, moist environment is a place the dog or cat can reach to scratch starting with an occasional itch and progressing into a potentially serious allergic dermatitis. Not all ear problems are due to allergic reactions; however, many dogs and cats will develop fungus or bacterial infections and/or ear mite infestations within the ear. These causative agents, once they are diagnosed, are relatively easy to treat and cure. Drops that contain the appropriate ingredients, such as, parasiticides, antibiotics and sometimes corticosteroids to relieve the itching are utilized and are frequently successful in controlling skin allergies due to ear problems. Once the ear problems are cleared up, the itching subsides and the scratching stops. Demodectic and Sarcoptic mange mites are causes of itchy skin and subsequent scratching in dogs. These mites burrow under the skin and lay eggs feeding on the skin as they do so. Demodectic mange can cause hair loss in the flank and sides of the dog creating lesions to both sides of the dog’s body uniformly. Sarcoptic mange is a zoonotic disease, meaning it can be transmitted to humans. I can recall years ago when a rather affluent family came to my practice with three toy poodles that were scratching incessantly. The dog’s bodies were red and inflamed with severe hair loss. Both adults in the family and their teen-age daughter also reported skin lesions on their abdomens, as well as the housekeeper who spent a great deal of time with the dogs. At the time, therapeutic shampoos and chemical dips with insecticides were utilized to rid both dogs and humans of these parasites as was the case with this family for a complete cure in both dogs and family members. Cats are rarely infested with these mites.

The most common cause of dermatitis in dogs is flea bite dermatitis. When the flea bites, it secrets a protein through its mouthparts that prevents the blood from coagulating so they can extract a blood meal. Many dogs and cats develop a reaction to this protein which can cause a severe allergic dermatitis. A flea infestation with just a few fleas can cause scratching by the pet to the extent that the pet causes self-inflicted skin rash or irritation. Sometimes, if left untreated, these irritations become infected causing major sores, usually on the rump area of the dog or cat. Other signs of flea-bite dermatitis include fever, loss of appetite and incessant scratching that leads to further skin damage. Severe flea infestations can lead to anemia due to the loss of large amounts of blood. The life cycle of fleas includes the egg, larvae and the adult fleas. At normal room temperature, the entire life cycle can occur in about 18 days; however, void of optimal conditions, fully formed fleas can remain in their cocoon stage for up to 12 months. This is a reason why current science dictates that flea season lasts all year, and most external parasites on pets should be treated and managed continuously. In order to control the flea population, a vigorous management process must be put in place on the pet, in the house and in the yard or any other location that the pet may frequent. New and safer, more effective products aimed at controlling adult fleas on pets have made flea management possible without pesticide sprays, shampoos and dusts in most situations. Once fleas infest a home, control will require a vigilant program that includes vacuuming, eliminating fleas on pets, and cleaning and treating areas outdoors where pets frequent. Newer products to control fleas on dogs and cats are applied either orally or topically to the body of the pet and are much more effective than the products that were available even a few years ago. Dr. Michael Dryden, Kansas State University College of Veterinary Medicine veterinary parasitologist, states that, “veterinarians can now prescribe a flea control product with residual speed of kill”, meaning that the product kills the flea before they have an opportunity to bite extensively. Dryden goes on to say, “we can now kill fleas fast enough where not enough protein is injected into the saliva of the flea to elicit an allergic reaction in the dog. We can manage flea allergies by using products with this residual speed of kill. We don’t know how many pets are affected by flea allergies, but that number is pretty high. It is the most common allergy in pets.” It is important to consult with your veterinarian about total management of the flea population when attempting to treat allergic dermatitis on your family pet. Many skin disorders, such as atopic dermatitis which are skin conditions of unknown causes, are influenced by the body’s immune system. Most immune mediated diseases including atopic dermatitis are chronic, inflammatory and proliferative. Conventional treatments include corticosteroids and immune suppressant treatments and have been used for decades. These treatments have been effective in improving the symptoms; however, both steroids and immune suppressors have shown complications and side effects with long term application and can be major obstacles to this treatment. There has been some evidence that certain probiotics can help to alleviate these side effects by shortening the length of treatment with immune suppressors, but more work is needed to substantiate that claim (Lin, et al). Other immune mediated skin disorders can be allergic reactions due to contact with pollens, dust mites, mold spores or food allergies. Sublingual immunotherapy, an important breakthrough for allergic veterinary patients, is currently being studied in field trials by veterinary dermatologists. One such study is being conducted by Dr. Thomas Lewis II of Dermatology for Animals in Gilbert, Arizona. Dr. Lewis states, “There are some dermatology patients who have failed injectable immunotherapy who have a positive response to sublingual immunotherapy. The response can occur more quickly. Rather than waiting for months to see a response to injectable immunotherapy, veterinarians often see improvement to sublingual administration in 30 days or less. There are also improved safety factors with sublingual treatments.” Obviously, if the treatment is scaled back for a length of time, the propensity for side effects should be minimized with this newly tested treatment modality.

Food allergies are a major factor in allergic dermatitis in dogs and cats. To uncover which food or ingredient may be causing the allergic reaction, there needs to be a family commitment to a diet trial to ascertain which food or ingredient is causing the allergic response. To stay on track with these diet trials, all dietary information provided by your veterinarian must be followed precisely. Feed your pet only the prescribed diet with no other foods or treats allowed. It is imperative that all family members and friends that may be in contact with the pet must be informed and participate in the feeding trials. Provide no treats, flavored products such as medications or chew toys unless they contain the prescribed ingredients. Do not let your dog or cat eat dropped food either while the family is eating meals in the house or outside from garbage containers, dropped food by passersby or any other source. This trial may take as much as eight weeks of feeding the special diet before clinical improvement is realized. Should the ingredient with which the pet had an allergic reaction is reintroduced into diet, the symptoms will probably reoccur. Only symptoms are alleviated, the underlying allergic reaction remains, many times for the life of the pet.

Veterinarians need to determine what is happening to the skin before therapeutic strategies can be employed. It takes a new, healthy skin cell about four to six weeks to mature and be present near the skin surface; therefore, even curable allergic dermatitis cases may take weeks to resolve. For the cases that are not curable, symptomatic signs can be reduced or alleviated altogether; however, should the allergen return, the symptoms will most likely reoccur at some level for the rest of the pet’s life. Because an itchy pet may be suffering from a food, airborne allergy, reaction to insect bites or allergies of unknown causes, it is important that your veterinarian knows all about the life your pet lives including what he or she eats. Do these symptoms exhibit themselves seasonally when the pet goes outside or when the pet travels to other locations? To confirm or rule out possible allergic triggers, veterinarians will order tests. The doctor may call for skin scrapings or serum tests to identify airborne allergens as the source of the reaction. Regardless of what caused the problems, tests are required to determine the most effective treatment for your pet. The quicker the diagnosis is made, the less symptoms the pet will exhibit. And that makes for a happier pet, as well as a happier family with less thump, thump, thump during the sleeping hours!


Bruce W. Little, DVM