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Why is my dog so itchy?

Why is my dog so itchy?

There are a number of reasons that dogs will be itchy and scratch themselves. Parasites, like lice, mites, and fleas can cause a great deal of discomfort for a dog, but today I would like to focus on allergies. Allergies are easily the top cause of itchiness in dogs that I see in my practice. Dogs can have allergies to things in their environment, like grasses, weeds, and trees. They can also be allergic to things in their food. I’d like to talk about both of these in a little greater detail in this post.

There are a number of reasons that dogs will be itchy and scratch themselves. Parasites, like lice, mites, and fleas can cause a great deal of discomfort for a dog, but today I would like to focus on allergies. Allergies are easily the top cause of itchiness in dogs that I see in my practice. Dogs can have allergies to things in their environment, like grasses, weeds, and trees. They can also be allergic to things in their food. I’d like to talk about both of these in a little greater detail in this post.

Environmental allergies

Unlike people, who usually manifest allergy symptoms with runny noses and sinus congestion, dogs will exhibit allergies to environmental allergens most often with itchy skin.  Most commonly, we will see what is called a “contact dermatitis”, where the area of the body that is contacting the allergen (grass, etc.) is the area that becomes pruritic (itchy).  We see this happen to dogs that like to lick or chew their paws.  They are likely contacting something in their environment that is causing a contact allergy to their feet, making them itchy.  Dogs who lay in the grass can also have a contact response on other areas of the body. 

Dogs can also be affected by inhalant allergies.  So, even if there is no direct contact with an allergen, like grass, dogs can inhale particles (pollen, etc.), which causes an immune system reaction in the body.  These immune complexes, which are the allergen particles bound to one of the body’s own immune system cells, becomes trapped in the capillary beds of the skin, causing an itchy response.  These reactions can happen anywhere on the body, making inhalant allergies very difficult to distinguish from contact allergies.

The other characteristic of environmental allergies is that they tend to be seasonal.  Pine pollen allergies are most common in the spring, so if your dog is itchy in the spring but not during other times of the year, this is most likely an environmental allergy.

Food allergies

Many dogs that suffer from prolonged bouts of itchiness can actually be reacting to ingredients in their food.  Much like the inhalant allergies discussed above, the body will form immune complexes with the offending allergen, and those will typically cause a reaction in the skin resulting in the itch response.

The most common ingredients in food that dogs will react to are the protein ingredients, with chicken and beef leading the list of most common offenders.  Unfortunately, most dog foods use one or both of these ingredients because they are the least expensive protein sources.  Ingredients like corn and grains, which may have significant effects on people, have not been shown to have similar effects on dogs.  There is a great deal of slick marketing and misinformation out there on dog food ingredients, so be careful where you search for your information!

While environmental allergies tend to be seasonal, food allergies tend to be year-round.  This can often be the distinguishing feature to help us decide which allergy may be more likely for your pet and which treatment area we wish to start first.  Recurrent ear infections and anal gland irritation are also frequent signs of food allergies.

Diagnosis and Treatment

Diagnosing the cause of allergies can be a difficult and frustrating process, for owners and veterinarians alike.  If environmental allergies are suspected, a blood allergy test can be performed to identify allergens that your pet may be allergic to.  Some allergens, like trees, weeds, and grasses are difficult to remove from an animal’s environment, especially if there is an inhalant component.  Some items that we test for can be removed from an animal’s environment, though. 

A significant number of dogs have dust mite allergies.  Removing old furniture, mattresses, and carpeting can be enough to clear some dogs of their allergy symptoms.  Another environmental allergen that affects a significant number of dogs are food storage mites.  There are actually tiny little mites (tyrophagus and acarus sp.) that live on all dry cereal grain products.  This includes dry dog food, and even human foods we eat like cereal and breads (gross, right?).  These mites can be killed by freezing, so some dogs may be able to be treated by pre-packaging kibble into single-serving bags and freezing them.  Allowing the food to thaw a few hours before serving will make it a little easier to eat but still have the effects of killing the storage mites.

For dogs with environmental allergies that cannot be treated by removing the allergen from the environment, we can have allergy injections formulated to treat the allergies.  These formulations are similar to allergy injections taken by people who have allergies.  They are designed to gradually desensitize the pet’s immune system to the allergen over time.  For those who may be a little squeamish about injections, there are now oral spray formulations that can be used.  These allergy injections or oral preparations are effective for most dogs.

If a pet has year-round itchiness, then we may elect to investigate a possible food allergy before allergy testing.  Unfortunately, there is not an accurate way to test for food allergies, so we are left to a trial-and-error process with different diets to determine if an allergy exists. 

The first type of hypoallergenic diet is called a novel protein diet.  Since proteins are the most likely ingredient to cause an allergy, switching a patient to a diet made with a different protein is often successful in relieving the allergy symptoms.  Novel proteins include fish, duck, rabbit, kangaroo, etc.  The waters have been muddied in recent years, though, by the emergence of hundreds of new food companies who like to use some of these ingredients in their diets and treats, so our chances of finding a protein source that a dog has never been exposed to before are becoming lower and lower.  Also, a lot of the over-the-counter food brands may promote themselves as a “fish and potato” diet, but if you scan the ingredient list, you may see some chicken or beef somewhere lower on the list.  Ingredients such as “animal protein” or ‘animal by-product” are also a clever way for companies to sneak other protein sources into a food without you knowing (until now!).

Because of the difficulty in assessing the novel protein diets, a superior way to perform a diet trial is with a hydrolyzed protein diet.  These diets can take any protein source (most commonly soy), and break those large protein molecules into smaller amino acids chains.  With these hydrolyzed (smaller) protein molecules, the body’s immune system does not latch on and attack the protein molecules and the allergic reaction is avoided.

These diet trials are not quite as easy as they sound to this point, however.  It can take as long as 2-3 months to get rid of all of the old allergens from the body, so we don’t know for that amount of time if the new diet is working or not.  Also, ALL other food sources must be eliminated from the diet for those 2-3 months.  This includes treats, table scraps, sneaking to the cat’s bowl for a snack, droppings from the toddler’s high chair, etc.  Even a small number of treats or a lick of your plate of leftovers can be enough to interfere with a diet trial.

After the 2-3 months have gone by, and if your dog has improved, we can do what is called a “challenge”, where we give some of the old diet to see if a reaction returns.  While this may seem silly to risk all of the benefits of 2-3 months of hard work and the dog feeling better, it is necessary to confirm this was the source of the allergic response.  There are so many other uncontrollable factors (e.g., environmental) that could have influenced the pet’s itchiness over such a long time span, that this confirmation step is often necessary to make sure we have the right diagnosis and treatment in place.

Other Therapies

While I have made this all sound relatively cut-and-dry with respect to the diagnosis and treatment of allergies in dogs, we still have a significant population of dogs that may not have relief after the steps outlined above.  Dogs with combination allergies (food and environmental) can be much more difficult to pinpoint and treat. 

There are also some dogs that are still itchy, no matter what else we do.  These dogs will undoubtedly have been checked for some of the parasites we touched on at the top of the article, and we see some that follow all of the recommendations with environmental allergies, including the injections, and go through a hypoallergenic diet trial and are still itchy.  For these dogs, we believe there is an inherent immune system abnormality that makes them itch, but we do still have some options for those in this category.

Cyclosporine is a medication that is designed to weaken the body’s immune system response so that the itching can be controlled.  This can potentially weaken the body’s resistance to other diseases, but is generally tolerated well with few side effects if the pet is otherwise healthy.

Oclactinib is a newer medication that can be taken twice a day to block the itch pathway.  While this medication does not address or treat the underlying allergy, it can block the pathways to the brain that result in itching, giving the pet relief from itching and scratching.  This medication is still relatively new, but has been shown to be very safe, even for long-term use, in clinical trials.  One drawback to this medication is its availability.  The manufacturer of this medication did not anticipate what its popularity would be, making this medication difficult to find and keep in stock for most vets.  So, keeping a patient on an uninterrupted supply can be difficult. 

Prednisone, a steroid, can be a very potent and successful medication in the relief of the symptoms of an allergy.  It is often used for immediate symptomatic relief of itching, but is not a good choice for long term relief due to the potential for side effects.  Weakening of the immune system (to a greater degree than cyclosporine), weight gain, increased thirst and urination, increased predisposition to diabetes and adrenal gland problems are all potential side effects of using prednisone, either repeatedly as a symptomatic relief agent, or for long-term relief.

Antibiotics and antifungal medications are also often used, especially in short-term symptomatic relief.  Many dogs that present to us with an acute allergy flare-up will have secondary skin infections that need to be treated, or else these will continue to contribute to the dog’s itchiness.  Often, an initial workup will consist of a short course of steroids or oclactinib to stop the itching, and antibiotics and/or antifungals to treat secondary skin infections.  Other diagnostic tests, such as the blood allergy testing or a food trial can then be initiated while the pet is returning to a good comfort level.

Antihistamines, like Benadryl and Claritin, can also be used to help the symptoms of allergies.  Typically, these can help reduce itching in milder cases of allergies, but for most dogs with more severe allergies, these medications won’t be sufficient as stand-alone treatments. 

Summary

So, allergies as a cause of itching in dogs is quite a complex area of veterinary medicine.  But, with a logical and systematic approach, we can find an underlying cause or find a treatment option that will work for you and your pet!

 

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