What Makes Our Pets Itch?
by Dr. Robert Dann, DVM | Nov 01, 2012
“My dog stays up all night scratching herself!”
Itchy skin, known as “pruritus,” is one of the most common reasons people seek out veterinary care for their furry friends. Although there are many causes of pet itch, the vast majority of cases of pruritus are attributed to a few main ones: allergy, external parasites and adverse food reactions or hypersensitivity. These primary diseases often affect the integrity of the skin, paving the way for secondary causes of itch such as infections or dry skin. Let’s go into the primary problems in more detail.
When animals are allergic to something around them, it often affects their skin. One of the country’s largest pet insurance companies cites skin allergies as the second most common claim made for dogs and the fifth most common claim for insured cats. Allergens absorbed through the skin or, less commonly, inhaled or swallowed, will cause a hypersensitivity reaction in the skin, known as “atopic dermatitis” or “atopy.” Symptoms often begin as redness and proceed to the animal licking, chewing, scratching or excessively grooming itself. In dogs, atopy-related pruritus occurs most commonly in the paws, face, groin, flanks, armpits and ears, with ear infections a common complication. In cats there is no usual pattern with atopy. Hair loss can occur from excessive licking or scratching and scabby eruptions in the skin, known as miliary dermatitis, are not uncommon.
Depending on what it is our pets are allergic to, their symptoms might be seasonal. If pollen is the offending allergen, we can expect itchy pets during the non-winter months. With an unseasonably warm winter in 2012, I received many calls in February and March from clients whose dogs were rubbing their faces, chewing their paws and scratching excessively due to the early arrival of tree pollen. However, if the allergy is to something found indoors – such as dust, dust mites or household mold – the scratching might occur year-round.
Fleas. Yes, they are dreaded. And for good reason! The most common parasitic cause of pruritus in cats and dogs is the flea, and considering that one insect can bite hundreds of times in a day, a single flea has the potential to wreak havoc on your pet’s skin.
When a flea bites, its saliva is injected into an animal’s skin where a protein in the saliva can act as a potent allergen. A flea-allergic pet can remain severely itchy for many days after a small number of flea bites, so all allergic pets need rigorous, continuous protection from flea bites. Ruling out the possible presence of fleas is paramount in any itchy pet.
There is a simple test that can be performed at home to check for evidence of fleas. With a pet in a sitting position in the bathtub or on a table or counter, vigorously rub the lower back and tail base area up and down with your fingers. If a pet has fleas, there probably will be flea droppings in these areas. When rubbed, these droppings (essentially little specks of flea-digested blood from your pet) will fall to the surface. Take a flat, moistened paper towel and holding it by two corners, pull it over the surface where your pet had been sitting. The flea droppings will appear as little black specks that smear out bloody on the wet paper towel.
Mildly infested pets are pretty easy to treat, but with heavy infestations, the pet and its environment must be treated. Other parasitic causes of pruritus in pets, much less common than fleas, are various forms of arthropods known as mange mites, lice or chiggers. Your veterinarian will be able to identify these parasites with a few simple tests and a microscope.
Food hypersensitivity is a non-seasonal allergic reaction to food or additives in the diet. It can occur in pets at any age, including very young pets and elderly pets that have consumed the same diet for many years. In cats there is no classic pattern of lesions, but pruritus abounds. Redness, hair loss, scabs and crusts may be seen on the torso and limbs, or may be confined to the head and neck areas. In dogs, pruritus can occur anywhere, including the ears and rear end.
Diagnosing food hypersensitivity can only be done accurately by utilizing a strict elimination diet. It is necessary to feed a diet containing only one source of protein and one carbohydrate. Food can either be prepared at home or a prescription diet can be purchased from your veterinarian and must not contain any food or additive that was included in a previously fed pet food. This includes treats, table scraps or the flavoring agents used in pet medications. Elimination diets must be adhered to strictly for 10 to 12 weeks. Be wary of commercially available “hypoallergenic” diets, as many have tested positive for items not suitable for diet trials. Such trials are best conducted under close supervision from your veterinarian as meticulous attention to detail is necessary for success.
Multiple primary causes of pruritus can occur simultaneously, unfortunately, and each may lower the threshold for itch for the others. As an example, a pet that is food-allergic may be more severely afflicted when a seasonal pollen allergy occurs, or a pet suffering from a seasonal allergy may react much worse to flea bites than it would in the winter time when there is no tree or grass pollen.
As mentioned earlier, the primary causes of pruritus will often set the table for secondary or “perpetuating” causes of itch, such as infection. Allergic pets are more susceptible to bacterial (most notably Staph infections) and yeast infections (known as Malassezia). These often recur on the skin, paws and in ears, which can greatly worsen your pet’s pruritus. Ear infections, for instance, are reported by a major pet insurance company as the most common claim for dogs. The vast majority of these ear problems are secondary to a flare of the allergy. Signs of an ear infection in a canine companion can include head shaking, scratching at the ears, excessive wax production, redness, thickening or swelling of the ear canal and bad odor. Infections must be treated when they occur, and more importantly, the allergy needs to be controlled or discomfort will continue and infections will recur, potentially developing antibiotic resistance.
The best source of information for diagnosing and treating your itchy pet will be your veterinarian. Once a diagnosis of the etiology of pruritus is made, therapies to bring it under control can be prescribed. Many classes of medications, both systemic and topical, can effectively treat allergy. Avoidance of the allergen is the treatment of choice if possible, such as with food or flea bite allergy. Allergy vaccine (as injection or more recently by mouth) is the only treatment that may alter the course of pets with atopic dermatitis.
To keep pets comfortable, symptomatic treatments can be used which range from mild (antihistamines, medicated baths) to aggressive (corticosteroids and the drug cyclosporine), with the latter having greater risk for side effects. When parasites are the cause of itch, they can be targeted with very specific products readily available for each particular parasite.
An itchy pet can be frustrating to treat, but the vast majority can be managed very successfully, restoring their comfort and quality of life. And yours!
The author wishes to thank board certified veterinary dermatologist, Dr. Cecilia Friberg, for reviewing this article.