"My dog won't stop scratching" is a typical lament around here in the fall. We see itchy dogs all year but it is more common now. Last week, I often had several appointments in a row for itching. It can be frustrating. The dog is usually uncomfortable. His people can't sleep with the collar jangling all night. Mange or infections may cause itching but allergic dermatitis, in its multiple forms, is the most common cause. Allergic dermatitis may be caused by food allergy, inhalant (atopic) dermatitis, contact dermatitis, bacterial (or Staph) hypersensitivity, or flea bite hypersensitivity. Or, put more succinctly, a dog’s skin may react to things they eat, anything they breathe in, anything they touch, their own bacteria, or bites from things that crawl on them, fleas being the most common.
It is commonly thought that food sensitivity is the biggest player in creating itchy skin. The true incidence of food allergy is 0.9% of cases. So, if we only approach the problem from a dietary perspective we are merely scratching the surface :). Food allergy is most often a non-seasonal problem. It is usually generalized over the majority of the body but doesn't really follow any specific pattern and can mimic other causes of itching.
Inhalant allergy, or atopic dermatitis, is an itchy skin reaction to things in the animal environment. These allergens were long thought to enter the body only through inhalation but we now know they can enter through the skin as well. When they enter through the skin, a breakdown of the normal epidermal barrier has occurred in that creature’s skin. The breakdown allows the allergen unwelcome entry to the animal’s immune system. These allergens may include things like grasses, pollen, shrubs, molds, cat and human dander, and dust mites. The potential list is lengthy. This allergy is often seasonal. It typically involves the feet, face and ears but not usually the back and up over the tail base.
Contact dermatitis is less common but includes specific skin reaction to things the animal touches. This may include grass and plants they run through, bedding, or the backing of carpeting. This allergy may or may not be seasonal. It usually affects the area under the forearms (axillary region), the groin (inguinal area), or the belly.
Bacterial hypersensitivity is a reaction to the normal bacteria on the skin. Any of the other allergies can lead to bacterial overgrowth and secondary infection. Bacterial infection and reaction are most common on the belly and inguinal region of the body. Certain breeds like the German Shepherd and Golden Retriever are more prone to bacterial infections in general.
Flea allergy dermatitis is the most common allergy we see this time of the year. Flea allergy may be seen any time of the year and we won't always find fleas, even when we know that they are the cause. An important distinction needs to be made between a flea infestation and a flea bite hypersensitivity reaction. A dog may be covered in fleas but not be reactive to them. Another dog may get a single flea bite and have his system react to the flea saliva from the bite. That dog may itch intensely for an extended period of time. This is a very important concept because when flea allergy is on our list of possibilities for your animal, we are going to recommend flea control whether we saw an actual flea or not. Flea hypersensitivity usually results in itching on the lower back and over the tail base and spreads down the back legs and on to the belly.
It is also important to consider that any given animal doesn't have to have just one of these causes. They often work in concert especially in dogs that we see multiple times during many different seasons of the year. It is quite common to see a flea allergy reaction in a dog with atopic dermatitis and a secondary infection. It is not surprising for that dog to also have food sensitivities. We also keep in mind that there may be other complicating factors in some patients. Concurrent yeast infections or hormonal imbalances, such as low thyroid may play a role.
This is the list of possibilities that runs through our heads when evaluating an itchy dog (the list is pretty similar in the cat, as well). Remember that flea allergy is very common. In the fall in the Northwest, if a dog has itching on their back and at the base of the tail, they have a flea allergic reaction until proven otherwise. This is true whether we find fleas or not.
So, keep your pet on flea control! This will avoid the most preventable itching.